Successful Dieting [1/5]– Lean Body Mass and The Importance of Exercise

Not all weight loss should be considered successful. A successful weight loss should be judged taking into account several factors such has the ratio of fat to lean mass lost - in other words, in a successful diet lean mass losses should be kept to a minimum. Exercise, especially weight training, can and should be used to offset lean mass losses during a diet, and in some cases make you lose fat and gain muscle at the same time.

One study assessed the individual and combined effects of weight loss and weight training on body weight and body composition for 8 weeks (1). Forty obese women were randomly assigned to 4 groups, a control (C); diet without exercise (DO); diet plus weight training (DPE); and weight training without diet (EO). Baseline caloric requirements were estimated and then reduced by 1000 kcal/d. The nutritionally balanced diet consisted of 50% carbohydrate, 27% protein, and 23% fat and included a daily protein supplement. C and EO subjects were instructed to maintain their normal caloric intake. Protein supplements were given to the two diet groups to ensure protein intake 1.0 g/kg body weight.

The weight training routine included the following exercises: bench press, inverse leg press, lateral pull down, biceps curl, triceps extension, calf raise, leg extension, and hamstring curl. Subjects went to failure on the third set: the exercise supervisor and the subject’s partner provided strong verbal encouragement during the final phase of the third set, and the subject’s partner helped lift the weight past any momentary weak points in the final set until the subject was unable to voluntarily complete another repetition.

Body weight decreased for all dieting groups, except for the exercise only group. Body weight decreased more for the diet only group (-4.47 kg) followed by diet plus weight training group (-3.89 kg) and the control group (-0.38 kg). The exercise only group gained a little weight (0.45 kg).

More importantly, lean body weight (LBW) increased with exercise only (1.07 kg) and diet plus weight training (0.43kg), compared with a decrease for diet only (-0.91 kg) and control (-0.31 kg). Upper-arm muscle areas increased for all groups with the greatest increase with diet plus weight training (11.2 cm2) and exercise only (10.4 cm2) compared with control (2.7 cm2) and diet only (2.1 cm2). In percentages of total body weight loss, diet only group lost about 20% LBM, and diet plus exercise lost 11% LBM. This study therefore concluded that adding weight training exercise to a caloric restriction program with 27% protein (1.0 g/kg) results in maintenance of LBW compared with diet only (1).

Increases in bench press strength were also observed with diet plus exercise (+5.31kg), with exercise only (4.77kg) and for the control (1.13kg), and a slight decreased with diet only (-0.69kg) after 8 weeks.

Other studies observed the same degree of LBW increases with exercise following an energy deficit. One study reported LBW increases of 0.5kg (2) and another reported an increase of 1.2 kg (3) over 16 and 17 wk, respectively. In the second study with 22 obese women (3), increased physical activity consisted of jog-walking 2.5 miles and 1 hr of calisthenics/week. Caloric restriction was self-determined and was generally moderate, accounting for about 60% of the total mean energy deficit. Importantly, many of the women had failed at previous attempts to lose weight by dieting alone.

However other studies reported loss of LBM even with exercise (4,5,6,7). Maintenance or even gain of LBM can be achieved with caloric restriction with aerobic (2) and weight training (1,3), although the mechanisms may be quite different. Maintenance of LBM may result from increasing the proportion of calories expended as fat and reducing the need to deaminate amino acids to supply carbohydrates or through muscle use (2).

Losses of LBW expressed as a percent of total weight lost have ranged from as little as 15% for mild caloric restriction (1,800-kcal) (8) to as high as 30-80% during semistarvation (600-800kcal) followed by 16 days of total starvation and 7 days back to the restricted diet (9) and 80% of maintenance calories or 600-1000kcal per day (4).

Diet-induced weight lost as FFM and fat mass is similar between older obese men (10) and obese women (11) compared to younger adults (11,12). As noted above, negative caloric balance induced by exercise or in combination with caloric restriction appears to minimize losses of LBM (1,2,3). Adding endurance or resistance exercise training to a diet program helps preserve FFM during weight loss (13,14,15,16).

A meta-analysis of studies conducted primarily in young and middle-aged adults also found that exercise reduced the percentage of weight lost as FFM from 22% in women and 29% in men to 17% for both women and men (17).

Obese older subjects were subject of 6 months of weekly behavioral therapy for weight loss in conjunction with exercise training 3 times per week (18). The diet contained approximately 30% of energy as fat, 50% as carbohydrate, and 20% as protein. Total calorie intake was adjusted to prevent more than a 1.5% loss of body weight per week, with the goal of 10% weight loss at the completion of the study. The exercise program focused on improving flexibility, endurance, strength, and balance. They lost about 8.4% of body weight without a change in fat-free mass. Additionally, compared with the control group they lost fat (-6.6kg) whereas the control group gain fat (1.7kg) (18).


The ability to lose fat and gain muscle at the same time in a caloric deficit is usually seen in the untrained obese, but as we will see in a future article it can be done for the trained athlete as well. 

Other factors will be discussed in the following articles, such as protein intake in a caloric deficit and the rate of weight loss. Finally, another feature of a successful diet comes in a long-term, the dieter should be able to maintain the weight loss (fat) and avoid fat regain.

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