Biology concepts and applications

¶ … aerobic exercise or resistance training to a very low calorie diet are Donnelly JE, Jacobsen DJ, Jakici JM, and Whatley JE, "Very low calorie diet with concurrent vs. delayed and sequential exercise" published in 1994 in the 18th volume at page 469 of the International Journal of Obesity and Related Metabolism Disorders (Donnelly et al.) and Bryner RW, Ullrich IH, Sauers J, Donley D, Hornsby G, Kolar M, and Yeater, R, "Effects of Resistance vs. Aerobic Training Combined With an 800 Calorie Liquid Diet on Lean Body Mass and Resting Metabolic Rate" published in 1999 in the 18th volume at page 115 the Journal of the American College of Nutrition (Bryner et al.). Both publications examined the hypothesis of whether the addition of either aerobic exercise or weight training to a very restricted diet increased various desirable measurements such as weight loss, fat free or lean mass body weight, and resting metabolism of the subjects.

The Donnelly et al. study found that neither the aerobic exercise nor the weight training had a significant effect on weight loss or the ratio between weight loss and fat free mass. Only the resting metabolism rate of the group that did both aerobic exercise during the diet and weight training subsequently had a very small (6.1%), but significant, increase in baseline. The rest of the groups showed no significance difference in total weight loss or resting metabolism rate. Thus, the conclusion of the paper was that the addition of aerobic exercise or weight training did not appear to have a clinically significant effect for people following very low calorie diets.

In contrast, the Bryner et al. study determined that the addition of aerobic exercise or weight training had significant but differing effects. The addition of aerobic exercise significantly increased the weight loss of the participants on the diet (4.7%) compared to the group doing resistance training and controls. However, almost the entire difference can be attributed to loss of lean body mass (4.0%). The addition of resistance training avoided any loss of lean body weight, but did result in less overall weight loss. Further, those using resistance training had a significant increase in resting metabolic rate (19.2%). Based on these results, Bryner et al. concluded that the addition of resistance training to those on a very low calorie diet would have two desirable effects: (1) help preserve lean body mass and (2) increase resting metabolism rate.

The scientific method was used in the two papers in very similar manners. Both groups observed the amount of weight loss for people on very low calorie diets and wondered if it could be increased by the addition of aerobic exercise or weight training. Both appear to have begun with the hypothesis that these added activities would have positive effects on particular measurements such as total weight loss and resting metabolic rate. Lean body mass was measured in both studies to better interpret the total weight loss results. Both studies had at least three groups of participants, those on the diet alone, those on the diet plus the aerobic exercise, and those on the diet with weight training. The studies were begun with preliminary measurements of body weight, resting metabolic rate, and lean body mass, among others, for groups of people on very low calorie diets. Donnelly et al. looked at 113 people (all female), while the Bryner et al. study was much smaller, with only 20 people (17 women, 3 men). After performing the required diet or diet plus exercises for 12 weeks, both studies did follow-up measurements of the same variables. As discussed fully above, the two studies came to opposite conclusions about the clinical value of aerobic exercise and resistance training during very low calorie diets.

A significant difference between the two studies, and the probable reason for the differing results, was the variation between the exact resistance training program that was followed. Although the two studies did approximately the same amount of aerobic and weight training (4 training sessions per week of aerobic training and 3 days per week of weight training), the actual weight training exercises done were different. The Bryner et al. study emphasized the use of progressively increasing weights and used ten weight lifting stations, while the Donnelly et al. study did not increase the weight over time and used only five weight lifting stations. This difference alone could easily explain the differing results. It appears that the program that was used in the Donnelly et al. study might not have been intense enough to result in the increase in lean body mass that would alter resting metabolic rates. If the aerobic exercise program used was similarly less intense, this could also explain why there was no difference in the weight loss measured between those doing aerobic exercise and those on the diet alone. These observations would tend to make the Bryner et al. study more reliable, given that they utilized as sufficiently intense exercise program to see the results on weight loss, lean body mass, and resting metabolic rate that would be predicted from this physical work.