Markers of dietary protein intake are associated with successful weight loss in the POUNDS Lost trial

Abstract

To assess the association of markers for dietary protein intake, measures of dietary adherence and demographic variables with weight loss in the POUNDS Lost study over the first 6 months and again between 6 and 24 months using data from those who completed each period. This is a secondary analysis of pooled data on completers assigned to one of four diets: 65%C/15%P/20%F (AP/LF), 55%C/25%P/20%F (HP/LF), 45%C/15%P/40%F (AP/HF) or 35%C/25%P40%F (HP/HF) in the POUNDS Lost study. Urinary nitrogen excretion, dietary adherence measured by 24-h recall and attendance at sessions, age (above and below 50 years), gender, race/ethnicity and activity by pedometry were analysed. Increased spread between protein intake at baseline and protein at 6 or 24 months, assessed by urinary nitrogen excretion, was associated with greater weight loss from baseline to 2 years. At 6 and 24 months, older age, male gender, body mass index > 30 kg m^-2 and adherence to the fat and protein diets were associated with more weight loss. None of these variables was associated with a regain from 6 to 24 months. Weight regain for women in the highest carbohydrate (65%) group was significantly greater (-4.4 kg [95% CI: -5.9, -3.0]) than for women in the lowest carbohydrate group (-1.8 kg [95% CI: -3.2, -0.4 kg]) (P for interaction = 0.012). An increased spread in the difference between baseline and follow-up protein intake was associated with greater weight loss, consistent with the 'protein spread theory'. Women eating the highest carbohydrate diet regained more weight from 6 to 24 months.

Keywords: High protein diet; low-carbohydrate diet; randomized clinical trial; urinary nitrogen excretion.

Figure 1

Weight change from baseline to 6 months for each individual participant in the 4 dietary assignment groups ranked from the largest loser on the left to the most weight gain on the right. Panel A (n=38 ) is the AP/LF group (15% protein, 20% fat, diet, 65% carbohydrate; Panel B (n=43 ) is the HP/LF group (25% protein, 20% fat, 55% carbohydrate); Panel C (n=28 ) is the HP/LF group (15% protein, 40% fat, 45% carbohydrate); and Panel D (n=30) is the HP/HF group (25% protein, 40% fat, 35% carbohydrate).

Figure 2

Change in body weight by quartiles of urea nitrogen/creatinine excretion. Panel A is the change in quartiles urea nitrogen/creatinine excretion from baseline to 6 months (quartile 1 is −58.7g/g to −14.2g/g; quartile 2 is −14.2g/g to 0.93g/g; quartile 3 is 0.93 g/g to 19.7 g/g; quartile 4 is 19.7g/g to 282.7g/g); Panel B is the change in quartiles of urea nitrogen/creatinine excretion from baseline to 24 months (quartile 1 is −62.9g/g to −10.9g/g; quartile 2 is −10.9g/g to 2.4g/g; quartile 3 is 2.4g/g to 23.0g/g; quartile 4 is 23.0g/g to 201.8g/g).

Figure 3

Mean weight loss from baseline to 6 months and from 6 months to twenty-four months in females and male according to macronutrient assignment. For the 102 women on the lowest carbohydrate diets, significantly less weight loss was observed; weight change was −1.8% (95% CI −3.2%, −0.4%), significantly different from men [−5.5% (95% CI −7.2%, −3.7%)] (p=0.0016) and significantly less in women on the lowest carbohydrate diets [−4.4% (95% CI −5.8%, −3.0%)] (p=0.0116). Women lost significantly less weight (−3.2% [−4.3, −2.2]) on the low fat diets than men (−6.0% [−7.3, −4.6]) (p=0.0015), but the low fat macronutrient comparison combines the two highest carbohydrate diets (65% and 55%).