WHYBROW, STEPHEN, CLAUS MAYER, TERRY R. KIRK, NIK MAZLAN, AND R. JAMES STUBBS. Effects of two weeks' mandatory snack consumption on energy intake and energy balance. Obesity. 2007;15:673-685. Objective: Our goal was to compare the effects of mandatory consumption of commercial snack products (CSPs) on energy intakes and energy balance in free-living adults and to assess the interaction between habitual level of CSP consumption and the interventions. Research Methods and Procedures: Four groups of 18 subjects (lean and overweight, males and females) were studied using a crossover design. Subjects consumed one type of CSP (high-carbohydrate, high-fat, or mixed composition) at three manipulations of energy 0 MJ (control), 1.5 MJ (low-energy), and 3.0 MJ (high-energy) each day during three 14-day interventions. The study design was parallel for type of CSP (macronutrient composition) and withinsubjects for energy level. Subjects self-recorded food intakes between Days 8 and 14, and body weights were investigator-recorded on Days 1, 8, and 15 of each intervention period. Daily energy expenditure was estimated by heart rate monitoring. Results: Daily energy intakes increased from 10.4 MJ (control) to 11.1 MJ (low-energy) and 11.5 MJ (high-energy) (p Ͻ 0.001), resulting in a trend (not significant) for body weight gain. Energy balance was more positive when subjects were not recording their food intakes than when they were (p Ͻ 0.001). There was a trend (not significant) for greater increases in energy intake with increasing fat content, and energy density, of the interventions. Frequent CSP consumers compensated more for the interventions than did infrequent CSP consumers (R 2 ϭ 0.125, p ϭ 0.003). Discussion: Subjects partially compensated for energy when supplemented with CSPs over 14-day periods, although this was insufficient to prevent some increase in energy balance. The level of compensation correlated with habitual energy intake from CSPs.

The view of carbohydrates in relation to obesity has changed over the past few decades from being conducive to overconsumption and weight gain to being protective. This article reviews the mechanisms by which carbohydrate is purported to protect against weight gain. Although carbohydrate is metabolized and stored in the body less efficiently than fat, when de novo lipogenesis is invoked on very high carbohydrate diets, the beneficial effect on energy balance is likely to be minimal when typical high fat Western diets are consumed. However, it has been suggested that high carbohydrate foods may influence energy balance by reducing food intake through greater satiety effects, reducing energy density and displacing fat from the diet-the fat-sugar seesaw effect. To date, there seem to be few differences between sugars and starches on satiety and energy intake, but few studies have examined this. Some reduced-fat, and, therefore, higher carbohydrate, foods are highly energy dense. High carbohydrate foods do not necessarily have a low energy density. Evidence from recent studies suggests that adding carbohydrate, and especially sugar, to the diet neither displaces fat from the diet nor protects against elevated energy intake. Although it is easier to overeat on high fat than low fat foods, simply replacing fat with carbohydrate in the diet may not be as protective against overconsumption as the energy density or fat-sugar seesaw arguments suggest.

Objective: To develop and test an experimental model designed to detect changes in selection between foods individually enriched in protein, carbohydrate and fat in human subjects. Design: Randomised counterbalanced (Latin square) design. Setting: The metabolic suite at the Rowett Research Institute's Human Nutrition Unit. Subjects: 16 normal-weight men (mean BMI 23.5). Interventions: Subjects were each studied 4 times in a 2-day protocol. On day 1 subjects received a ®xed maintenance diet; on day 2 they received a mandatory intake as breakfast (08.30) plus a drink at 10.30. This comprised 80% of resting energy requirements as high-protein (HP), high-carbohydrate (HC) or high-fat (HF) foods (60% of energy in each case) or an equal mixture (M) of macronutrients, 33% by energy. All mandatory treatments contained the same energy content and density. From 12.30 onwards, subjects had ad libitum access to a counter-balanced selection of three groups of familiar foods (10 HP, 10 HC and 10 HF; 30 foods in total). Most energy in each food was derived from one macronutrient ( $ 60%), the remainder being equally split between the other two macronutrients. Results: Subjects were signi®cantly less hungry before lunch on the HP and M (33% protein) treatments (F 3Y44 7X35; P`0.001). At lunch, they ate more energy after the HF treatment than after any of the other treatment (F 1Y38 9X00; P 0.005). This was largely in the form of fat and protein, and to a lesser extent carbohydrate. Subsequent energy intake (EI) were lower on the HF treatment, largely through selection of less fat in the afternoon (F 1Y42 6X90; P 0.012). Daily EIs were similar across treatments. Conclusion: This design appears sensitive meal-to-meal to changes in both nutrient and EIs. Sponsorship: This work was supported by the Scottish Of®ce, Agriculture, Environment and Fisheries Department.

Objective: To examine the effect of increasing the variety of sensorially distinct but nutritionally identical foods on appetite, food intake and body weight, over 7 days, in men. Design: Six younger, lean men (mean (s.d.) age 27.0 (2.9) y; weight 74.7 (3.9) kg; height 1.78 (0.03) m; body mass index (BMI) 23.6 (1.1) kgam 2 ) and six older, overweight men (mean (s.d.) age 39.7 (2.9) y; weight 89.2 (4.4) kg; height 1.78 (0.04) m; BMI 28.1 (0.5) kgam 2 ) were each studied three times during a 9 day protocol, whilst resident in the Human Nutrition Unit. On days 1 ± 2, subjects consumed a medium fat (MF) maintenance diet (40% fat, 13% protein and 47% carbohydrate by energy) calculated at 1.6 Â resting metabolic rate (RMR). On days 3 ± 9 subjects had ad libitum access to MF foods (550 kJa100 g) with every item the same macronutrient composition and energy density. Subjects had continuous ad libitum access to 5, 10 or 15 food items per day on the low-variety (LV), medium-variety (MV) and high-variety (HV) treatments, respectively. The order of treatments was randomized across subjects. Subjective hunger was tracked hourly during waking hours using visual analogue scales (VAS). Body weight (as a proxy of changes in energy balance) was measured before eating and after voiding, each morning. Results: Food and energy intake of the 12 men increased as the variety of foods increased, giving mean energy intakes of 10.13, 11.00 and 11.89 MJaday on the LV, MV and HV treatments, respectively (F(2,20) 10.32; P`0.001). This effect was ascribable almost entirely to the lean men. Energy intake amounted to 1.57, 1.76 and 1.97 Â RMR in the lean men and 1.33, 1.40 and 1.45 Â RMR, for the overweight men on the LV, MV and HV diets, respectively. Weight changes amounted to À0.16, À0.28 and 0.43 kg (lean) À1.03 and À1.52 kg and À0.66 kg (overweight), on the LV, MV and HV diets, respectively. The overweight men may have constrained their energy intake relative to expected requirements. This may have been due to a congnitive effect or an age effect. There was no signi®cant group or diet effect on subjectively rated hunger. Conclusions: These data suggest that increasing the variety of sensorially distinct foods that are virtually identical in composition can increase food and energy intake and in the short to medium term can alter energy balance. Sponsorship: This work was supported by the Scottish Of®ce.

No abstract