3. Combined Therapy (Diet and Physical Activity)

Twenty-three RCT articles investigated the effects on body weight of a combination of a reduced calorie diet with increased physical activity. The control groups used diet alone or physical activity alone. 

Of the 15 studies deemed acceptable, each of them compared the combined intervention with diet alone (346, 365, 375, 377, 380, 384, 434, 435, 445, 448, 469-473), and 6 of them also compared the combined intervention to physical activity alone (346, 365, 375, 434, 448, 474). The studies varied in terms of the length of the active intervention period as well as the length of the follow-up. Many of the programs lasted for more than 6 months, and five studies had intervention or follow-up data for at least 1 year (346, 375, 380, 445, 473). Two studies included patients with type 2 diabetes (470, 473). Participants in the diet and physical activity group most often participated in supervised group-based physical activity consisting of 30- to 60-minute sessions 3 times a week, and they were encouraged to maintain a maximum heart rate between 60 and 80 percent. There were three diet components: general dietary advice, caloric reduction of 500 to 1,000 kcal per day, or a diet containing 1,200 kcal per day.

Rationale: Of the 15 RCT articles, 12 observed that the combined diet and physical activity group had a mean greater weight loss of 1.9 kg (4.2 lb) and a mean greater BMI reduction of 0.4 (range of 0.3 to 0.5) than the diet-alone group (346, 365, 375, 377, 380, 384, 434, 435, 448, 469, 470, 473). One study compared different forms of physical activity in combination with diet and found that, compared to diet alone, the greatest weight loss occurred when the combination intervention included both aerobic and resistance training: 0.9 kg (2 lb) greater weight loss than aerobic exercise plus diet (435). Another study reported that participants receiving resistance training in combination with diet had 2.2 and 5.0 kg (4.9 and 11 lb) greater weight loss than the diet-alone group after 24 and 48 weeks, respectively (469).

Five of the six studies that compared combined intervention with physical activity alone observed that the combined intervention group had a 5.3 kg (11.7 lb) (range of 3.6 to 6.2 kg) (7.9 to 13.7 lb) greater weight loss and 0.9 change in BMI unit than the physical activity-alone group (346, 365, 375, 434, 448). This greater weight loss was significant in three studies (365, 375, 448).

Three RCTs compared the longer term versus the shorter term effects of the combination of physical activity and diet versus diet alone (384, 469, 473). All three studies found that the combination resulted in approximately 1.5 to 3 kg (3.3 to 6.6 lb) greater weight loss than diet alone over the longer term of 9 months to 2 years.

Rationale: Three RCTs (365, 375, 471) that examined the combined effect of diet and physical activity on weight loss also had measures of abdominal fat, as measured by waist circumference. Two of the three RCTs showed that the combination intervention resulted in greater reduction in waist circumference than diet alone in men (365, 375) and (only one) in women (375). In the other RCT, no differences in reduced waist circumference were observed (471).  Of the three RCTs comparing combination therapy to physical activity alone, one study reported a greater waist reduction of 2.7 to 3.8 cm in women and men, respectively (375), and by less than 1 cm in another study (365).  The effects of combination therapy on abdominal fat in these studies are not separable from the effects on weight loss.

Rationale: Nine RCTs examined the effect of a combination of diet and physical activity on fitness compared to diet alone (346, 375, 377, 380, 434, 435, 445, 448, 475). In most studies, the physical activity was in the range of 60 to 80 percent VO2 max. All nine RCTs showed that a combination of diet and physical activity improved cardiorespiratory fitness, as measured by VO2 max, more than diet alone, whether reported relative to body mass in ml O2 /kg/min or in absolute values by ml O2 /min (346, 375, 377, 380, 434, 435, 445, 448, 475). Studies of longer duration tended to show the greatest improvement. This improvement was significant in six of the studies (346, 375, 377, 380, 434, 448).