Food Intake, Energy Balance and Body Weight Control

E Doucet and A Tremblay

Physical Activity Sciences Laboratory, PEPS, Laval University, Ste-Foy, QueÂbec, Canada, G1K 7P4

Obesity is a multifactorial and complex affectation that is characterized by a long-term excess energy intake (EI) above energy expenditure (EE). Since fat oxidation seems to be dependent on SNS activation and also seems to remain acutely unaffected by fat intake, this macronutrient is certainly partly responsible for this situation. In addition, high-fat intake does not induce as potent satiety signals or a compensation effect on subsequent EI as do diets rich in carbohydrates or proteins. Moreover, since alcohol intake acutely inhibits fat oxidation and does not promote subsequent compensation for its energy content, it should consequently be regarded as a substrate which can induce a positive energy balance under free-living conditions. Thus, in a weight reducing context, each energy substrate should be manipulated while taking into account its speci®c characteristics. Obesity has also often been associated to a decreased sympathetic nervous system (SNS) activity, hence sympathomimetic agents have been proposed as a possible way to partially correct this situation. Two of these agents are the widely consumed caffeine (CAF) and the pungent principle of hot red pepper, capsaicin (CAP), which acutely increase EE and reduce EI under some circumstances. Furthermore, other factors like dietary ®bers, that have been shown to increase satiety and fullness, and reduce EI in some cases, should also be considered. Descriptors: obesity; energy balance; macronutrients; alcohol; sympathomimetic agents; dietary ®bers

Introduction characterized by a positive fat balance which more often than not leads to body weight gain. Thus the reduction of EI The prevalence of obesity in af¯uent societies is reaching as dietary fat is being increasingly targeted as a possible epidemiological proportions and even if our understanding way to reduce or better control one's body weight. Conse- and knowledge of the causes leading to obesity are ever quently, it has been repeatedly proposed that lowering fat increasing, health professionals cannot seem to reverse this intake might be bene®cial to a weight maintenance pro- situation. Obesity is being characterized as a long term gram (Lissner et al, 1987; Flatt, 1991; Kendall et al, 1991; energy imbalance, that is energy intake (EI) being greater Thomas et al, 1992; Westerterp, 1993; Astrup et al, 1994a). than energy expenditure (EE). Many studies have shown This phenomenon has led the food industry into the era of that nutritional and food-related non-nutritional factors low-fat products. in¯uence the adjustment of EI to EE. The main objective The association between high-fat diets and obesity is of this report is to describe the effects of some of these also frequently observed in both animal and human studies. factors with the intent to propose strategies that would The animal models have clearly established that high-fat enable health professionals to further improve their inter- diets have a profound effect on body weight and composi- vention in obese individuals. tion (Hill et al, 1991; Racefas et al, 1992), even under isocaloric conditions (Boozer et al, 1993). In humans, the failure of fat intake to acutely promote fat oxidation (Flatt Fat et al, 1985; Flatt, 1988; Schutz et al, 1989; Bennett et al, The ever increasing pool of data concerning the speci®city 1992; Jebb et al, 1996) and the fact that fat oxidation seems of the characteristics of each macronutrient urges the to be dependent on SNS stimulation (Acheson et al, 1988a; clinician wishing weight reduction or maintenance to no Tremblay et al, 1992) could be factors explaining why longer address EI without also looking into macronutrient high-fat foods favor a positive fat and energy balance. composition (Table 1). In that respect, fat intake seems to Furthermore, it was demonstrated that the post-obese state have the most impact on energy balance. Indeed, popula- might be characterized, to an even greater extent, by a tion studies have, on numerous occasions, shown a positive decrease in lipid oxidation under high-fat diet conditions association between fat intake and adiposity (Dreon et al, (Astrup et al, 1994a; Raben et al, 1994a; Ballor et al, 1988; Romieu et al, 1988; Tremblay et al, 1989; Colditz et 1996). However, it was also demonstrated that obese al, 1990; Miller et al, 1990; Klesges et al, 1992; Tucker & women have a greater fat oxidation than the non-obese, Kano, 1992). Furthermore, industrialized countries, like the and that this condition might be the result of an adaptation United States where dietary fat intake provides from 31.9± to high-fat diets to promote long-term fat balance and body 36.9% of total daily EI for adults of both sexes and all weight stability (Schutz et al, 1992; Astrup et al, 1994b). major ethnic groups (NHANES, 1988±1991), are generally The observation that fat intake fails to stimulate fat oxidation when given as a supplement to a basal meal does not seem to explain differences in daily EE observed when this macronutrient is isoenergetically substituted by carbohy- Correspondence: Dr A Tremblay. drates. Accordingly, it was reported that the substitution of Received 3 June 1997; revised 19 June 1997; accepted 13 August 1997 complex carbohydrate by dietary fat has no effect on EE Food intake and body weight E Doucet and A Tremblay 847 Table 1 Energy substrate characteristics

Characteristics Alcohol Fat Carbohydrates Proteins

In¯uence on subjective No Lesser effects than Compared to fat: Greater Better than other substrates feelings of hunger and satiety Tremblay 96 proteins or CHO Rolls 88 Yes No effect Lawton 93 Blundell 93 Hill 90 Poppitt 96 Blundell 93 Lower van Wyk 95 Rolls 94 Rolls 91 No Stubbs 95 Foltin 90 de Graaf 92

Potential to exert compensatory No Lesser effects than Compared to fat: Better than other substrates effect on EI Tremblay 96 proteins or CHO Greater Yes Poppitt 96 Lissner 87 Rolls 94 Partial Tremblay 89, 91 Stubbs 95 Hill 86 Foltin 93 Rolls 94, 95 Same as fat DeCastro 88 Stubbs 95 Rolls 91 Barkeling 90 Foltin 90, 92 Bingham 94 Ability to promote its oxidation High Low High High Shelmet 88 Flatt 85, 88 Flatt 78 Nair 83 Weststrate 90 Schutz 89 Acheson 84 Dauncey 83 Prentice 92 Bennett 92 Lean 88 Suter 92 Jebb 96 Schutz 89 Astrup 92 Energy density High High Low Low Intake associated with increased Yes Yes No Yes risk of weight gain Kroumhout 83 Dreon 88 Toubro 97 Buemann 95 Suter 92 Romieu 88 Jeffry 95 No Tremblay 95 Tremblay 89 Lyon 95 DeCastro 88 Cigolini 96 Colditz 90 Bingham 94 Miller 90 No Klesges 92 Fisher 85 Tucker 92 Coldtiz 91 Sonko 94 Liu 94 Effect of b-adrenergic blockade NA No changes Decrease No changes on oxidation Acheson 88 Acheson 88 Acheson 88 Tremblay 92 Tremblay 92

CHO carbohydrates. NA data not available.

even if there was a change in substrate oxidation (Roust et nounced preference for this macronutrient are factors that al, 1994). Furthermore, a high-fat low-carbohydrate weight can potentiate weight gain under high-fat conditions. There maintenance diet did not reduce 24 h EE compared to its is also growing evidence that dietary fatty acid composition isoenergetic high-carbohydrate low-fat diet counterpart might play a role in this matter. Results from animal studies (Abbott et al, 1990). have shown that rats fed a saf¯ower oil (78.6% polyunsa- There is also a growing body of evidence concerning the turated fat (PUFA), 11.4% monounsaturated fat (MUFA) effects of fat on food intake and its ability to induce satiety. and 9% saturated fat (SFA)) diet as opposed to a beef Indeed, it has been demonstrated that high-fat diets give tallow (2.1% PUFA, 47.4% MUFA and 48.9% SFA) diet, way to overconsumption (Lissner et al, 1987; Tremblay et accumulated less body fat, had lower respiratory quotient, al, 1989; Tremblay et al, 1991; Stubbs et al, 1995) because demonstrated higher DIT (Shimomura et al, 1990), and fat seems to have a lesser effect on satiety than do other higher SNS activity in brown adipose tissue (Takeuchi et macronutrients (Blundell et al, 1993; Lawton et al, 1993). al, 1994). Moreover, the higher body fat accumulation In addition, dietary fat seems to have a lesser potential to under the beef tallow condition seems to be due to a exert negative feedback on subsequent EI than do carbohy- decreased SNS activity in rats (Matsuo et al, 1995). In drates (Rolls et al, 1994; Stubbs et al, 1995) or proteins humans, it has been reported that the proportion of satu- (Stubbs et al, 1995). High-fat preloads even seem to exert a rated to unsaturated fat possibly affects the net contribution lesser effect on subsequent EI of obese compared to of fat to EE (Jones et al, 1985), and it was demonstrated normal-weight individuals (Rolls & Hammer, 1995). that DIT was greater for the high-PUFA to SFA ratio (1.25) Another factor which can further potentiate weight gain is than for the low-PUFA to SFA ratio (0.25) diets (Jones & the increased preference for fat in obese and post-obese Schoeller, 1988). It was also shown that the increase of individuals (Drewnowski & Greenwood, 1983; Drew- dietary PUFA results in an increase of the oxidation of nowski et al, 1992). medium and long-chain fatty cids (Clandinin et al, 1995). The reduced capacity of fat to acutely promote its Furthermore, it was reported that the isoenergetic substitu- oxidation, its decreased satiating power and the observation tion of long-chain triglycerides by medium-chain triglycer- that obese and post-obese seemingly have a more pro- ides (MCT) had an inhibitory effect on food and EI (Stubbs Food intake and body weight E Doucet and A Tremblay 848 & Harbron, 1996) and that incorporation of MCT into the normal weight unrestrained females and obese restrained diet stimulated thermogenesis (Seaton et al, 1986; Hill et and unrestrained females as rated by the Cognitive al, 1989; Scal® et al, 1991). Restraint Scale of the Stunkard Eating Inventory even if normal weight unrestrained males showed a quite accurate compensation for energy content of the different preloads Carbohydrates (Rolls et al, 1994). Accordingly, a recent experiment It is generally well recognized that populations who con- mimicking free-living conditions in which three different sume a greater proportion of energy in the form of diets varying in macronutrient composition (20, 67 and carbohydrates are leaner than those who do otherwise. 13%; 40, 47 and 13%, and 60, 27 and 13% for fat, This might be partly due to the fact that a high amount carbohydrates and proteins respectively) showed that car- of energy in the form of carbohydrates for a few days is bohydrates and proteins seem to have a greater potential to needed to induce de novo lipogenesis (Acheson et al, exert negative feedback on EI than does fat (Stubbs et al, 1988b) compared to the impact of a high-fat intake which 1995). However, there is also a considerable body of seems to produce an immediate positive fat balance (Flatt evidence that does not support the above proposed effects et al, 1985). Another interesting observation is that people of carbohydrates on food intake. In that respect, it has been who had been vegetarians for a long period of time had a demonstrated that either low or high-carbohydrate (1.8 vs resting metabolic rate that was 11% higher than their 3.5 MJ), or low or high-fat (1.8 vs 3.5 MJ) preloads at omnivorous counterparts, although this difference disap- lunch have the same satiating power. Moreover, this study peared when controlling for carbohydrate, and fat intake also demonstrated that subsequent EI over the remainder of and norepinephrine (Toth & Poehlman, 1994). In previous the day was not signi®cantly affected by either manipula- studies by the same group, it was demonstrated that male tion of macronutrient or energy content (Foltin et al, 1990). vegetarians also had a tendency toward higher resting These results are in agreement with those of Rolls et al metabolic rate (RMR) than the typical north-american (1991) who failed to show any signi®cant differences dieter (Poehlman et al, 1988; Oberlin et al, 1990). This is between responses in food intake following ingestion of a an interesting observation since it has been documented high-carbohydrate (81% of 0.9 MJ) or a high-fat (65% of that carbohydrate intake seems to stimulate SNS activity 0.9 MJ) preload (Rolls et al, 1991). Furthermore, it was (Acheson et al, 1984a). The greater SNS activity under shown that there is clear evidence for subsequent caloric high-carbohydrate intake condition might be partly respon- compensation when energy content was manipulated, but sible for the greater RMR and the effects of carbohydrates equicaloric manipulations of macronutrient, namely carbo- on thermogenesis. hydrate and fat content, failed to show differences in In this regard, it has been reported that DIT of carbohy- subsequent EI (Foltin et al, 1992). drates is equivalent to approximately 10% of EI (Flatt, Even if the data concerning the effects of carbohydrates 1978) and that during carbohydrate overfeeding studies, on satiety and hunger and also on thermogenesis are quite 24 h EE increased from 10±40%. In a recent review, a low- abundant, those surrounding the impact of an ad libitum fat high-carbohydrate diet was proposed to lead to a greater high-carbohydrate low-fat diet on body weight loss or EE than its high-fat, low-carbohydrate counterpart (Wes- maintenance are scanty. However, in a very recent study terterp, 1993). Indeed, it would seem that carbohydrates from Toubro & Astrup (1997), it was shown that after an have a greater potential to increase thermogenesis possibly initial weight loss ( 12.6 kg) induced by energy restricted due to the obligatory cost of glycogen storage (Acheson et diets and sympathomimetic agents, subjects who were al, 1984b). It was later demonstrated that carbohydrate given free access to a high-carbohydrate low-fat diet over intake promotes carbohydrate oxidation (Schutz et al, a period of one year maintained more of the initial weight 1989), that a high-carbohydrate-containing diet produced loss (8.0 kg vs 2.5 kg) than did the group who were given a greater DIT than the high-fat diet (Lean & James, 1988) ®xed energy intake ( 7.8 MJ/d). These results are in and that a high-carbohydrate diet administered to post- accordance with those of Jeffry et al (1995) who found obese women caused an increase in 24 h EE that was that under low-fat high-carbohydrate conditions, subjects entirely generated by an increase in carbohydrate oxidation lost 2.5 kg vs 0.5 kg for the calorie-counting group after an (Astrup et al, 1992). intervention period of 12 months. Furthermore, it was Carbohydrates exert a stimulating effect on thermogen- demonstrated that adherence to a low-fat high-carbohydrate esis whereas its effects on satiety and food intake do not diet was strongly correlated to body fat loss (Lyon et al, yield as clear a trend. A recent study showed that when 1995). Conversely, it was reported that a ®xed energy comparing the effects of equicaloric preloads (1.2 MJ) of intake was better at producing weight loss (10 kg vs either carbohydrates, proteins or fat in ten normal-weight 6 kg) than what was observed under ad libitum low-fat women, carbohydrates and proteins had a greater satiating diet conditions (Schlundt et al, 1993). power than did fat (Rolls et al, 1988). The latter results are Another important issue related to the impact of high- in accordance with those of Blundell et al (1993) who carbohydrate intake pertains to the enhancing effect of this demonstrated that in lean subjects a high-carbohydrate macronutrient on its own utilization. It might be argued that breakfast ( 87% of 3.36 MJ) suppressed hunger ratings the increase of carbohydrate oxidation observed under high- and energy intake signi®cantly more than the equicaloric carbohydrate diet conditions is also responsible for the high-fat one ( 57% of 3.36 MJ) in a mid-morning snack inhibition of fat oxidation observed under such conditions served 90 min after the preload whilst no signi®cant which could be detrimental to weight stability. This is differences were found between conditions at lunch time somewhat unlikely because of the relatively low amount of which was served 270 min after the preload (Blundell et al, fat consumed under high-carbohydrate conditions and also 1993). Moreover a high-carbohydrate preload ( 80% of because of the effects of carbohydrates on thermogenesis. 1.5 MJ) had a greater suppression power over subsequent Moreover, satiety seems to be reached with a lesser amount food intake than did the high-fat preload ( 70% of of calories under high-carbohydrate conditions which is 1.5 MJ) in normal weight restrained males and females, probably the most likely explanation for the inability of Food intake and body weight E Doucet and A Tremblay 849 high-carbohydrate diets to induce lipogenesis and ultimately Weight loss is normally associated with a decrease in body weight gain under free-living conditions even if this RMR which can be partly attributable to the decrease in fat type of regimen does to a certain extent inhibit fat oxidation. free mass (FFM). However, weight loss under high-protein, very low-calorie diet (VLCD) has been shown to produce a decrease in FFM (17%) that is lesser (Barrows & Snook, Proteins 1987) than what would be expected under a typical VLCD The effects of proteins on EI and EE, and ultimately on (1/3 decrease in FFM and more) (Holloszy, 1974). It was body weight control are probably the lesser considered of reported that a severe hypoenergetic diet (2.1 MJ) can all macronutrients, but there is an increasing pool of data produce signi®cantly more weight loss than a hypoener- concerning this issue. DeCastro & Elemore (1988) demon- getic regimen (4.2 MJ) without the expected decrease in strated that in subjects self-reporting their food intake for RMR when isonitrogenous conditions are preserved for 7 d, proteins were the most ef®cient macronutrient at both diets (Stanko et al, 1992). In addition, maintaining suppressing food intake independently of their contribution protein intake to its usual level during energy restriction has to EI. Accordingly, it was reported, via a 16 d weighed been shown to signi®cantly reduce the fall in sleeping dietary record by post-menopausal women, that proteins metabolic rate and 24 h EE (Whitehead et al, 1996). were the only substrate that was negatively correlated to In summary, protein intake seems to have a comparable food intake (Bingham et al, 1994). However, these results effect, if not more potent, on the subjective feelings of are not supported by another observational study in which hunger and satiety as does carbohydrate intake. The same protein intake seemed to be signi®cantly associated with can be said about its in¯uence on subsequent EI and more adiposity (Buemann et al, 1995). thermogenesis. Furthermore, the preservation of FFM Experimental data also suggest an existing relation during weight loss when a high-protein intake is maintained between the protein content of diet and food or energy is another factor that urges clinicians to look at the protein intake. Different preloads of proteins (0.4, 1 and 1.7 MJ) component with more scrutiny, especially in a weight had no signi®cant effect on subsequent food intake, nor did reduction context. different preloads of carbohydrates or fat (deGraaf et al, 1992). However, there is a considerable number of studies Alcohol that provide discordant results. In this context, obese as well as normal-weight individuals have been shown to In the recent past, the contribution of alcohol to the average signi®cantly decrease their subsequent EI by 19 and 22%, american diet was approximately 5.6% of the total EI respectively, when the effects of a high-protein meal (54% (Block et al, 1985). This represents a contribution to EI of 2 MJ) were compared to that of an isoenergetic high- which is not trivial and whose role in the regulation of carbohydrate meal (63% of 2 MJ) (Hill & Blundell, 1986). energy balance is still a matter of controversy. Accordingly, it was demonstrated by the same authors that In an early study, Gruchow et al (1985) demonstrated a high-protein meal produced greater subjective feelings of that the calories from alcohol were additive in the diets of fullness and a greater decrease in the desire to eat than did light to moderate drinkers. However, in the same study, an isoenergetic high-carbohydrate meal (Hill & Blundell, alcohol energy was also shown to replace the calories from 1990). It was also shown that high-protein and high- other macronutrients in the diets of heavy drinkers. Other carbohydrate isoenergetic lunches produced a reduction studies have also demonstrated that alcohol derived calories of EI at dinner that was 12% greater under the high-protein were additive, thus not replacing energy from other sub- lunch condition than for the high-carbohydrate condition strates (Jones et al, 1982; DeCastro & Orozco, 1990; (Barkeling et al, 1990). Accordingly, ingestion of a break- Tremblay et al, 1995b). fast (energy equivalent to 75% of basal metabolic rate) The observation that alcohol energy seems to be additive composed of either 3.1 MJ of protein, carbohydrate or fat to the EI from other energy substrates is in agreement with resulted in a signi®cantly greater decrease in hunger sensa- the fact that alcohol intake may exert a poor inhibitory tion between breakfast and lunch for the carbohydrates and effect on subsequent food and energy intake. Accordingly, proteins when compared to the fat condition (van Wyk et it was shown that a high-fat and alcohol appetizer was al, 1995). Furthermore, this study also showed that the followed by an increased ad libitum EI even after their protein breakfast was better at suppressing hunger over a high-energy density was controlled (Tremblay & St-Pierre, 24 h period in a calorimeter. 1996). Alcohol consumption also seems to have no effect It is generally well recognized that protein stores on satiety and fullness when taken concomitantly with a represent a precisely regulated compartment. It was high-fat meal. In addition, no compensatory effect of the reported that amino acid oxidation changes rapidly in excess energy associated to alcohol intake was observed for response to changes in amino acid intake in the way the subsequent meal (Tremblay & St-Pierre, 1996), which that substrate availability seems to be the primary determi- is in accordance with a recent study that demonstrated that nant of substrate oxidation. Thus, the net effect of this the consumption of an alcoholic beverage taken before a mechanism is a conservation of nitrogen when protein meal had no compensatory effect on the energy content of intake is low and in contrast, a high protein intake leads the following meal (Poppitt et al, 1996). These results are to loss of amino acid, nitrogen and carbon (Young & consistent with those from an earlier study which showed Marchini, 1990). that an alcoholic beverage taken at four different times The effects of proteins on EE are in agreement with the during the day resulted in a weak compensatory effect idea that protein balance is precisely regulated. Indeed, DIT (37%) of its own energy content (Foltin et al, 1993). of proteins has been shown to be greater than for its Many studies have investigated the role of alcohol in isoenergetic substitution by carbohydrates or fat (Nair et relation to energy metabolism. In an early study, Rosenberg al, 1983). Accordingly, the isoenergetic substitution of a & Durnin (1978) demonstrated that alcohol ingestion had high-carbohydrate diet by a high-protein diet resulted in a the same effect on resting metabolic rate as did other 12% increase in EE (Dauncey & Bingham, 1983). energy substrates, and that variations in RMR were prob- Food intake and body weight E Doucet and A Tremblay 850 ably more closely related to EI than to macronutrient evidence supports that alcohol seems to have a poor or composition of the diet. These results are in agreement no capacity to in¯uence subjective feelings of hunger and with those of more recent studies that showed that DIT of satiety, and also little in¯uence to promote compensation in alcohol is almost the same as it is for carbohydrates subsequent EI (Foltin et al, 1993; Poppitt et al, 1996; (Shelmet et al, 1988; Weststrate et al, 1990; Prentice et Tremblay et al, 1996). Furthermore, alcohol intake seems al, 1992). However, more recent results have shown that to favor alcohol oxidation at the expense of other energy DIT of alcohol is equivalent to approximately 20% of its substrates, especially fat (Shelmet et al, 1988; Suter et al, energy content (Suter et al, 1994) which is substantially 1992; Sonko et al, 1994; Murgatroyd et al, 1996). more than that of carbohydrates (Flatt, 1978). Even if the DIT of alcohol does not characterize it as an adipogenic Caffeine substrate, its effects on the oxidation of other substrates might. Indeed, alcohol acutely suppresses the oxidation of It has been estimated that 80% of adults in North America other substrates (Shelmet et al, 1988) and to a greater are regular coffee drinkers and that it is not uncommon for extent fat oxidation (Shelmet et al, 1988; Suter et al, 1992; an individual to consume 200±250 mg (the equivalent of Sonko et al, 1994; Murgatroyd et al, 1996). This suppres- approximately 2±3 cups of coffee) of caffeine (CAF) per sion might be due to the fact that alcohol calories become day (Sawynok, 1995). the primary source of metabolic fuel as a mode of detox- Evidence suggests that CAF has the potential to increase i®cation which might acutely inhibit the oxidation of other metabolic rate of lean individuals for up to three hours after fuel sources. ingestion (Acheson et al, 1980; Hollands et al, 1981; Another interesting feature of alcohol is the fact that it Dulloo & Geissler, 1989; Astrup et al, 1990; Yoshida et cannot be bodily stored. Despite this characteristic, numer- al, 1994; Bracco et al, 1995) and during the ®rst 12 h of a ous studies have tried to establish if alcohol intake could be 24 h stay in a metabolic ward after which no residual effect involved in the mechanisms leading to weight gain. The of CAF is detected (Dulloo et al, 1989). Moreover, it would results concerning this issue are surrounded by con¯ictual seem that women have a lesser acute thermogenic response reports. It was suggested that the habitual consumption of to CAF than do men (Perkins et al, 1994). alcohol in a moderate fashion in excess of energy needs The ability of CAF to alter substrate oxidation is also of might lead to a condition which favors lipid storage and major interest. Accordingly, it would seem that CAF that could consequently lead to weight gain over time ingestion produces an increase in lipid oxidation and in (Suter et al, 1992). It was also reported in an epidemiolo- the availability of free fatty acids for energy production gical study that of all energy substrates, alcohol was the (Astrup et al, 1990; Bracco et al, 1995). Furthermore, CAF only one positively correlated with body fatness and it was seems to directly stimulate in vivo lipolysis (Van Soeren et thus concluded that alcohol consumption might be an al, 1996). important factor in body weight gain (Kromhout, 1983). Some differences have been observed between lean Furthermore, the combination of alcohol and high-fat diets subjects and their obese counterparts with respect to CAF favors weight gain in the form of central subcutaneous fat responsiveness. It has been demonstrated that CAF does not (Tremblay et al, 1995a). The latter study is in agreement increase metabolic rate in obese individuals as it does in with recent results that have demonstrated that the increase lean (Astrup et al, 1990; Bracco et al, 1995), and that there of daily energy taken in the form of alcohol is positively are variations in CAF response among the obese population correlated to waist circumference, waist to hip ratio and (Yoshida et al, 1994). Moreover, it was shown that the probably visceral fat (Cigolini et al, 1996). In contrast, thermogenic effects of CAF can be prolonged over night in numerous studies have led to the conclusion that alcohol lean subjects but not in the obese, and that this effect is intake does not promote body fat storage (Fisher & Gordon, achieved with a normal CAF consumption (Bracco et al, 1985; Colditz et al, 1991; Liu et al, 1994; Sonko et al, 1995). However, it was reported that even if obese indivi- 1994) and that it does not, to an even greater extent, in duals have a lesser response to CAF, their lipid oxidation women (Colditz et al, 1991; Liu et al, 1994). Moreover, was nevertheless signi®cantly increased by ingestion of this individuals who drink alcohol consume more total daily compound (Bracco et al, 1995). In contrast, another study energy than those who are non-drinkers, but tend to weigh demonstrated that obese persons have the same sensitivity less which is possibly due to the inef®cacy in the utilization to CAF than do lean individuals when it is taken alone in of alcohol calories (Fisher et al, 1985). the fasted state, but they rather seem to have a de®cient The idea of an inef®cacy in the disposal of alcohol dietary-induced thermogenesis (DIT) which can be partly calories might be related to the hypothesis of a futile cycle corrected by addition of CAF to meals (Dulloo et al, 1989). as described by Lands & Zakhari (1991). This concept CAF also seems to exert an inhibitory effect on food suggests that the futile cycle employs an irreversible intake. Indeed, it was demonstrated that CAF has the oxidation of alcohol to acetaldehyde and a reduction of potential to reduce EI in men, but failed to produce the acetaldehyde to alcohol which can dissipate six ATP per same effect in women (Tremblay et al, 1988). The latter cycle thus eliminating any net gain of alcohol calories after study is supported by data which have clearly established two or three cycles. that CAF ingestion in rats reduces food intake and hence It is as of yet unclear how long term alcohol intake body weight gain (Racotta et al, 1994). affects bodily fat stores. It should however be taken into account that discordances observed between different cross sectional studies could be due to the fact that other lifestyle Capsaicin factors might contaminate the results. For instance, it is Decreased and/or de®cient SNS activity has been proposed possible that the inverse relation observed between alcohol as a possible factor leading to obesity. Thus, the inclusion intake and adiposity in women might be partly explainable of sympathomimetic compounds such as capsaicin (CAP) by better compensatory skills of this group under such into the diet might partially correct this situation. CAP is a conditions. This is likely the case since experimental pungent principle of hot red pepper that has long been used Food intake and body weight E Doucet and A Tremblay 851 for enhancing food palatability and medicinally as a coun- terirritant. Early studies with animals have shown that rats fed high-fat diets with added CAP gained less weight than controls, had lower plasma triglyceride levels (Kawada et al, 1986a) and oxidized more lipids (Kawada et al, 1986b). It was also reported that CAP might promote lipid mobi- lization from adipose tissue of rats during exercise, result- ing in a sparing of glycogen (Lim et al, 1995). Accordingly, it was demonstrated that CAP failed to produce changes in carbohydrate or glycogen metabolism at rest or during exercise in rats (Matsuo et al, 1996). Furthermore, the effects of CAP administration were subdued by the addition of a beta-blocking agent (Kawada et al, 1986b). In an early study with human subjects, Emery & Henry (1985) reported that when a meal is consumed with added red pepper, DIT is signi®cantly greater than after a control meal, 53 vs 28% increase in metabolic rate, respectively. Moreover, it has been demonstrated that a meal with red pepper signi®cantly increased respiratory quotient and produced a slight (10% over control) but not signi®cant increase in EE (Lim et al, 1997). In addition, red pepper ingestion would seem to increase carbohydrate oxidation more than it does for fat (Lim et al, 1997). The fact that CAP seems to stimulate carbohydrate oxidation in humans and fat oxidation in animals is puz- zling, but can probably be explained by methodological Figure 1 Illustration of the impact of dietary energy restriction on SNS/ PNS balance in obese individuals and potential contribution of exercise differences. The fact that most animal studies used cap and sympathomimetic agents in the follow-up of post-obese subjects. whereas human studies were conducted with red pepper might be partly responsible for the discordant results. Moreover, the fat content of diets used in animal studies could lead to a decreased EI; they promote chewing and was relatively high compared to the dietary fat intake of therefore require an increased effort to eat; they slow subjects involved in human studies. gastric emptying which might trigger satiety; reduce hunger It is very well established that sympathomimetic drugs and prolong fullness; they decrease digestive and absorptive can stimulate SNS activity in humans and animals. Since ef®ciency which might lead to an increased loss in fecal weight loss has been shown to produce a decrease in the energy; they are more satiating than their energy equivalent SNS/parasympathetic nervous system (PNS) ratio (Aronne low-®ber foods and they might carry nutrients further down et al, 1995), the manipulation of some environmental the ileum, which might trigger the ileal break that has been factors such as capsaicin, caffeine and exercise has, at the shown to reduce ad libitum food intake. Accordingly, evi- least, the potential to partly compensate for this effect. As dence suggests that obesity is much less prevalent in popula- illustrated in Figure 1, it would be useful to favor adaptations who consume ®ber-rich diets as opposed to those who tions in SNS/PNS balance which are compatible with a consume low-®ber diets and that animals normally eating weight maintenance prescription, especially in the post- diets rich in dietary ®bers become obese on low-®ber diets obese individuals. However, even if sympathomimetic (Van Italie, 1978; Leeds, 1987; Kimm, 1995). drugs and exercise both stimulate substrate oxidation and Many studies have tried to determine the impact of a energy expenditure, the selectivity of the effects of exercise high-®ber regimen on long-term energy balance and body needs to be discussed. It has been demonstrated that weight control. In this context, it was found that subjects postexercise EE and fat oxidation are mediated by an who had greater body mass index (BMI) values also had increase in SNS activity (Poehlman & Danforth, 1991; diets containing the most fat and the least dietary ®bers Tremblay et al, 1992). This increase in EE and fat oxida- (Medeiros et al, 1996). In addition, weight-reducing diets to tion might in turn be generated by an increase in b- which a dietary ®ber supplement had been added (5±6 g/d) adrenergic activity in skeletal muscle, such an effect not were shown to produce a greater body weight loss than the being observed in the heart (Plourde et al, 1991; Plourde et control diets (Rossner et al, 1987; Solum et al, 1987). al, 1993). In contrast, sympathomimetic drugs seem to Accordingly, a recent study on dogs showed that a activate all SNS mediated systems which not only results restricted low-fat high-®ber diet produced signi®cantly in an increase of EE and fat oxidation, but also of blood greater weight loss than its isoenergetic high-fat low-®ber pressure and heart rate. These observations emphasize the counterpart (Borne et al, 1996). On the other hand, a relevance of a stimulation targeting skeletal muscles rather dietary ®ber supplement (6.5 g/d) administered with a than a non-speci®c SNS activity which also affects cardiac 6.7 MJ/d diet, failed to yield any signi®cant bene®ts as function. far as weight reduction was concerned when compared to control diet alone (Rossner et al, 1988). Even if some doubts persist concerning the potential of Fibers an increase dietary ®ber intake to help better control body Dietary ®bers seem to have the potential to modify food weight, its effects on the subjective ®ndings of satiety, eating patterns and energy balance for the following rea- hunger and fullness has been well documented. Indeed, it sons: fullness might be associated with bulk because high- was shown that a low-®ber meal (3 g) was not less satiating ®ber diets have a greater volume than high-fat diets, which than a high-®ber meal (12 g) (Burley et al, 1987). However Food intake and body weight E Doucet and A Tremblay 852 fullness ratings were higher after the high-®ber meal than at factors which are most susceptible to reverse this with the low-®ber meal. In a more recent study, fullness phenomenon. Reducing fat intake while increasing carbo- and satiety were found to be signi®cantly greater after a hydrate intake would seem to be one of the most ef®cient high-®ber breakfast and to stay elevated for up to four methods to allow satiety while reducing EI. The reduction hours after consumption in both men and women (Turconi of alcohol intake should also be addressed, since it would et al, 1995). This is concordant with other studies that have seem that alcohol has a poor, or no capacity to in¯uence demonstrated that dietary ®ber supplementation (3.9±23 g) subjective feelings of satiety and hunger, and also little, or decreased hunger ratings (Rigaud et al, 1987), increased no in¯uence to promote compensation in subsequent EI. satiety as opposed to low-®ber diets (Raben et al, 1995), Alcohol intake also seems to promote alcohol oxidation at increased fullness and decreased the desire to eat (Raben et the expense of other macronutrients, especially fat. There- al, 1994b), and increased fecal energy excretion (Rigaud et fore, the effects of alcohol are typical of a substrate which al, 1987). can induce a substantial positive energy and lipid balance The type of dietary ®bers administered might have a role under free-living conditions and should be regarded as to play in relation to the mechanisms that might alter appetite such. and hunger ratings. Accordingly, it was reported that ad The documented effects of dietary ®bers on the sub- libitum food intake was signi®cantly reduced by psyllium jective feelings of hunger and satiety would seem to point gum (23 g) and psyllium gum combined to wheat bran toward their potentially interesting implication regarding (23 g) by 640 kJ/d and 481 kJ/d, respectively. However, energy balance. However, the effects of dietary ®bers on this effect was not seen with the supplementation of wheat these variables do not seem to be associated with substan- bran (23 g) alone (Stevens et al, 1987). In contrast, a high- tial changes in food or energy intake. One cannot overlook ®ber breakfast (20 g) of either soluble or insoluble ®bers the fact that the amount of dietary ®bers used in most signi®cantly reduced EI of the subsequent meal compared to studies very rarely exceeds 20 g/d. It is possible that in the low-®ber breakfast (3 g) despite the fact that total daily order to attain the expected decrease in food and energy EI intake was not affected by ®ber type or quantity. How- intake, one would have to increase to an even greater extent ever, it would seem that insoluble ®bers have the potential to ®ber consumption. Further research is needed to clarify this acutely increase feelings of satiety whilst soluble ®bers particular issue. would seem to produce greater satiety feelings 13.5 h after The fact that dietary fat oxidation seems to be dependent ingestion of breakfast (Delargy et al, 1995). In a more recent on beta-adrenergic stimulation (Acheson et al, 1988a; study from the same group, it was demonstrated that subjects Tremblay et al, 1992) is also of potential interest. More- consumed less energy (1.6 kJ vs 2.2 kJ, respectively) in the over, it would seem that the post-obese and obesity-prone acute period following a high-insoluble ®ber (22 g) break- individuals are often characterized by a subnormal resting fast compared with the high-soluble ®ber (22 g) breakfast. energy EE (Geissler et al, 1987) and a defective DIT Despite this difference in the acute phase, total daily EI did (Dulloo & Miller, 1986). This could probably be due to a not differ when both soluble and insoluble ®ber conditions decrease in SNS activity which could be partly responsible were compared, which is in agreement with the previous for the resistance to further reduction and/or maintenance study (Delargy et al, 1997). Another study showed that gel- of the adipose tissue mass in post-obese individuals, even if forming liquid ®bers favor a decrease in hunger, an increase these individuals are very often still overweight. In order to in fullness, and reduce the amount of food people actually counteract this situation, the manipulation of environmental wanted to eat, although it had no effect on food intake factors such as sympathomimetic drugs and exercise that (Tomlin, 1995). have the potential to elevate SNS activity would be useful. Even if dietary ®bers seem to in¯uence the mechanisms controlling food intake, they do not seem to increase DIT or alter substrate oxidation in any bene®cial way. Indeed, a high-®ber meal (26 g) failed to increase postprandial EE as did a non-supplemented meal test (8 g) (Scal® et al, 1987). Conclusions These results are in accordance with a more recent study in The literature summarized above tends to show that a which it was demonstrated that under isoenergetic condi- negative energy balance is favored by factors such as tions, subjects had a reduced DIT after a high-®ber meal low-fat/high-carbohydrate ratio, a high-protein and ®ber (25.5 g) as opposed to a low-®ber one (9.2 g). In addition, intake, an increase in PUFA intake and the incorporation of the high-®ber meal was associated with a decrease in fat food-related sympathomimetic agents. From a quantitative oxidation (Raben et al, 1994b). standpoint, the currently available data also permit to Evidence suggests that dietary ®bers have the potential conclude that the impact of some of these factors on to exert a suppressive effect on the subjective feelings of energy balance is more important than others. Figure 2 hunger and satiety. However, this effect does not seem to integrates our interpretation of literature regarding the necessarily translate into a decrease of food and energy potential effect of each factor on energy balance. In our intake. Even if the type of dietary ®bers (soluble vs opinion, the manipulation of the fat-carbohydrate contribu- insoluble) seems to affect the mechanisms leading to satiety tion to energy intake is the variable which seems to exert in different ways, the impact of dietary ®bers on EI seems the greatest impact on energy balance. The impact of to be more closely related to amount rather than form protein, alcohol and PUFA is also perceived important. ingested. The fact that dietary ®bers also seem to acutely Since the effect of a high-®ber regimen on EI has not yet inhibit fat oxidation deserves further consideration. been clearly demonstrated, its effect on energy balance and body weight remains uncertain. 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