. 1.Nitrogen balance, weight loss and resting metabolic rate were measured in thirty-eight obese inpatients on 2. All subjects were fed on 13% protein-energy in three rneals/d for the first week. 3. In weeks 2 or 3, using a cross-over design, ten subjects were fed on 15 or 10% protein-energy as three rneals/d; fourteen subjects were fed on five or one meal/d with 13%proteinenergy; and fourteen subjects were fed on 15% protein-energy as five mealsld or 10% protein-emergy as one meal/d. 4. N loss was least on the high-protein week and frequent-meal week: the largest difference was found when these effects were combined (P < 0.001). 5. When protein-energy was held constant at 13% N loss decreased significantly (P < 0.01) between week 2 and 3, but when the proteinenergy was manipulated there was no significant N conservation in the third week.This suggests that the protein:energy value is more important than meal frequency in the preservation of lean tissue. 6. Weight loss was also least on the 'high-protein' week and 'frequent-meal' week, but this result reached significance only when the effects were combined (P < 0.05). 7.Resting metabolic rate decreased with time but was not significantly altered by the dietary regimens.8. Therefore, during the first 3 weeks at an intake of 3.4 MJ/d, a diet with a high-protein concentration, fed as frequent small meals, is associated with better preservation of lean tissue than an isoenergetic diet with lower-protein concentration fed as fewer meals. There was no evidence that meal frequency or protein concentration affect the rate of fat loss. Cohn et al. (1963) showed that if one group of rats was fed ad lib., and a similar group of rats was force-pair-fed the identical diet in two meals/d, the force-fed rats gained more fat and excreted more nitrogen than the ad lib. control group. The higher the protein concentration in the diet, the more marked was the effect of force-feeding. This observation was linked with that of Fabry et al. (1964) who noted that there was an inverse relationship between the frequency of meals and adiposity in the population of Prague, and this has been confirmed in the Tecumseh study (Metzner et al. 1977). Mahler (1972) found that students who took a large carbohydrate supplement as a single meal gained more weight than when the supplement was divided in sixteen hourly fractions, but this result may be due to the order in which the tests were done, because the gorging protocol always preceded the nibbling one. Debry et al. (1973) compared the weight loss in 119 obese subjects who were given a reducing diet as either three or seven meals daily: the mean weight loss on seven meals/d was 142 g, but on three meals it was only 78 g/d. All these publications may be taken as support for the view that isoenergetic diets taken as a small number of large meals (gorging) are more fattening than the same diet taken as a large number of small meals (nibbling).From the viewpoint of energy balance it is difficult to understand why this should be so. If the diet ...

I . Weight loss, resting metabolic rate and nitrogen loss were measured in forty obese inpatients on reducing diets.2. Five subjects ate 3.55 MJ/d for 6 weeks (Expt I). Twenty-one subjects ate 4.2 MJ/d for the first week, 2.0 MJ/d for the second week and 4 2 MJ/d for the third week (Expt 2). Fourteen subjects ate 3.4 MJ/d for the first week and then 0.87 MJ protein or carbohydrate for the second or third weeks, using a cross-over design for alternate patients (Expt 3).3. Patients in Expt I had highest weight loss and N loss in the first z weeks, but adapted to the energy restriction over the remaining weeks. On average subjects were in N balance at the end of the study. 4. In Expt z patients eating 2.0 MJ/d in week 2 showed increased weight loss compared with week I . N loss was not raised but it failed to decrease as it had in Expt I. Weight loss and N loss were reduced on return to 4.2 MJ/d for a third week. 5.In Expt 3 patients eating 0.87 MJ protein showed significantly more weight loss and less N loss than patients eating 087 MJ carbohydrate.6. Resting metabolic rate decreased with time on the low-energy diet, but the manipulations of energy or protein content did not significantly affect the pattern of decrease.7. Both weight loss and N loss were greater the lower the energy intake, and both decreased with time. Diets with a high protein:energy value give a favourable value for N:weight loss at each level of energy intake.If the energy intake of an obese patient is reduced below the level of energy expenditure the energy stores of the body must decrease, and this is usually reflected in a decrease in bodyweight. The obese person has too high a fat:lean tissue value, so it is desirable that the weight loss should be mainly at the expense of fat. Since fat loss is a slow process, such patients yearn for treatment which will produce rapid weight loss. This can be achieved by treatments which cause the loss of water or lean tissue which are attractive to the patient in the short term, but only make matters worse in the long run. Resting metabolic rate (RMR) is the factor which chiefly determines how quickly obese patients can lose weight (Garrow et al. 1978) and this in turn is most closely related to lean body mass (Halliday et al. 1979) so treatment which causes excessive loss of lean tissue is self-defeating in the end. Calloway & Spector (I 954) made a comprehensive review of the effect of restricted energy and protein intake on N balance, and concluded that active young men in negative energy balance would inevitably be in negative nitrogen balance whatever the protein intake.

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The relationship between salivation, hunger, appetite, and estimates of energy intake was examined in female obese inpatients undergoing a course of weight reduction. On a constant low-energy intake (800 kcal/day) salivation, hunger, and appetite scores all declined. Estimates of energy intake did not. Sixteen different subjects were fed 1000 kcal/day for seven days, 500 kcal/day for seven days, and 1000 kcal/day for seven days. After acclimatization to the diet for a minimum of five days, salivation was directly related to energy intake; hunger and appetite ratings did not change significantly; and estimates of energy intake were sensitive to the decrease but not increase in energy intake. The limitations of each method of assessment are discussed.