Effect of exercise on energy intake and eating patterns in lean and obese humans.

Twelve obese and four lean subjects increased their energy expenditure by 100 kcal/day by cycling on a bicycle ergometer. The order of testing was alternated so that half of the subjects did exercise on the first three days and the remainder on the last three days. Ad lib energy intake was measured over six days using an automated food dispensing machine. The obese subjects ate 1196 +/- 517 kcal/day and the lean subjects ate 1162 +/- 301 kcal/day and showed no overall significant difference in energy intake or eating patterns. However, these obese subjects ate 18 kcal/day less and the lean subjects ate 155 kcal/day more during the exercise period. The difference in response confirms the hypothesis that lean subjects tend to regulate energy intake more accurately than obese subjects. Exercise increased the frequency of eating and drinking and decreased hunger and appetite for all subjects. There was a significantly greater decrease in hunger and appetite with exercise for the obese subjects. However, as there was no accompanying decrease in energy intake and some subjects had difficulty in completing the exercise, the value of small increases in voluntary exercise in the treatment of obesity is questioned.

The effect of covert changes in energy density of preloads on subsequent ad libitum energy intake in lean and obese human subjects.

1. Covert changes in energy intake were made by giving preloads of disguised energy density three times daily to 14 obese and 6 lean subjects. 2. The preloads contained 2.51 MJ (600 kcal)/d on days 2 and 3 and either 3.77 MJ (900 kcal)/d or 1.26 MJ (300 kcal/d) on days 4 and 5 and 1.26 MJ (300 kcal)/d or 3.77 MJ (900 kcal)/d on days 6 and 7. The order of testing was alternated for each subject. 3. Subsequent energy intake at each meal (lunch, dinner and breakfast) was measured with an automated food-dispensing machine. 4. Overall the obese subjects ate significantly less from the machine, 3.28 +/- 1.89 MJ (785 +/- 452 kcal)/d, than the lean subjects, 6.03 +/- 1.26 MJ (1442 +/- 300 kcal)/d. 5. Both groups of subjects adjusted their energy intake in the right direction to counterbalance the effect of the preloads but the lean subjects changed their intake by an average of 0.74 MJ (176 kcal)/d compared with the obese subjects who changed their intake by an average of 0.29 MJ (70 kcal)/d. 6. Although the lean subjects were better at adjusting their energy intake than the obese subjects, regulation was still imprecise relative to the 2.51 MJ (600 kcal)/d difference in energy intake that was imposed. 7. There were no significant differences in hunger or appetite between subjects or test situations.

The effect of increasing the relative cost of palatable food with respect to ordinary food on total-energy intake of eight obese inpatients.

1. It has been suggested that obese subjects have a greater relative preference for palatable foods than lean subjects. 2. The food intake of eight obese subjects was measured using an automated food dispensing machine. 3. Subjects ate ad libitum for the first three days from a range of acceptable foods predetermined by questionnaire. 4. On the next three days the food which subjects chose most frequently ('palatable' food) was priced at a level such that if the subjects maintained their intake of that food they were forced to reduce their total energy intake by 50 per cent, but the subjects were able to obtain food sufficient to maintain their energy intake only if they ate exclusively food rated as 'ordinary'. 5. On this differential fixed price schedule the obese subjects reduced total energy intake to a small extent (20 per cent) whereas their intake of palatable food was reduced to a larger extent (65 per cent). Thus obese subjects relatively defended energy intake at the expense of palatability. Hunger and appetite ratings did not differ from each other throughout the study.

Factors influencing the composition of the weight lost by obese patients on a reducing diet.

1. 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 1). 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 1 had highest weight loss and N loss in the first 2 weeks, but adapated to the energy restriction over the remaining weeks. On average subjects were in N balance at the end of the study. 4. In Expt 2 patients eating 2.0 MJ/d in week 2 showed increased weight loss compared with week 1. N loss was not raised but it failed to decrease as it had in Expt 1. 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 0.87 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.

The long-term effect of energy intake on salivation, hunger, and appetite ratings, and estimates of energy intake in obese patients.

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.

Factors determining weight loss in obese patients in a metabolic ward.

A metabolic unit is described in which it is possible to make controlled measurements of energy balance in patients with various types and degrees of obesity. Thirty-seven obese women were studied for three consecutive one-week periods on a diet which provided an average of 3.4MJ (800 kcal) daily, and some also undertook an exercise programme involving the expenditure of 850--1275 kJ (200--300 kcal) extra per day. The distribution of energy intake was varied from week to week, and within the day (nibbling and gorging), but neither these variations in dietary pattern nor the exercise programme significantly affected the total weight loss over the three-week study period. Very large variations were observed between individuals. Total weight loss over the three-week study period ranged from 1.6 to 9.8 kg. The best predictor of weight loss in a patient on a strictly controlled diet is the resting metabolic rate. The previous diet also affects weight loss: patients who had been keeping to a reducing diet before admission lost less weight, especially in the first week, than those who had not been dieting immediately before admission to hospital.