Low-fat vegan diet may keep extra pounds off

Overweight adults may lose the excess weight by adhering to a low-fat vegan diet, a study suggests.

“[Our findings show that] a low-fat plant-based dietary intervention reduces body weight by reducing energy intake and increasing post-prandial metabolism, apparently owing to increased insulin sensitivity resulting from reduced hepatocellular and intramyocellular fat,” said the researchers.

These findings address the need for interventions targeting overweight and obesity to prevent diseases that might develop from these conditions (eg, type 2 diabetes [T2D], metabolic syndrome), they added.

A total of 244 individuals (mean age 54.4 years, 87 percent female, BMI 28–40) were randomized 1:1 to either follow a low-fat vegan* diet (intervention arm) or make no diet changes (control arm) for 16 weeks. The intervention was supplemented by food samples and weekly classes for cooking demos and instructions. Daily alcohol intake was restricted to one and two in women and men, respectively. Usual medications and exercise regimens were to be maintained unless otherwise specified. [JAMA Network Open 2020;3:e2025454]

Week 16 saw a marked reduction in mean body weight in the intervention vs the control arm (–6.4 vs –0.5 kg; p<0.001). The researchers attributed this effect to the significant losses in fat mass (–4.1 vs 0.01 kg), lean mass (–2.1 vs –0.6 kg), and visceral fat volume (–216.5 vs –7.7 cm³; p<0.001 for all) in the intervention arm.

On subgroup analysis, the intervention arm saw reductions in hepatocellular lipid (liver fat; mean change, –0.8 percent; p=0.002) and intramyocellular lipid levels (muscle fat; mean change, –0.1 percent; p=0.03). The corresponding baseline values in the control arm did not change by week 16 (mean change, 0.3 percent and 0.13 percent, respectively).

The reduced fat build-up in the liver and muscle cells correlated positively with changes in insulin resistance (HOMA** index score, r=0.51; p=0.01 for both), as well as changes in fat mass (r=0.91; p<0.01 [liver] and r=0.51; p<0.05 [muscle]). According to the researchers, these effects may have contributed to improved glycaemic control and reduced insulin concentration.

“[B]y reducing [liver and muscle fat] levels, a plant-based diet may lead to increased mitochondrial activity and post-prandial metabolism,” they added.

Post-prandial energy expenditure did increase in the intervention arm by 18.7 percent by week 16, while no change was seen in the control arm (14.1 percent), generating a significant between-group interaction (p<0.001). Overall, the changes in post-prandial energy expenditure correlated negatively with changes in fat mass (r=−0.30; p<0.05), and positively with changes in PREDIM*** (r=0.36; p<0.05). “[This means that] as fat mass decreased and insulin sensitivity improved, post-prandial metabolism increased,” they explained.

“[The reduced fat levels are] particularly important because the accumulation of lipids in muscle and liver cells may also be associated with insulin resistance and T2D,” they added.

Despite evidence suggesting that meal composition influences post-prandial metabolism, [J Nutr Sci Vitaminol (Tokyo) 2005;51:355-360; Med Sci Sports Exerc 2004;36:709-716; Food Nutr Res 2010;doi:10.3402/fnr.v54i0.5144] the findings appear to show otherwise, as the study used identical test meals across all study phases. “[As such,] the increased post-prandial thermogenesis [may be] attributable to improved insulin sensitivity … [or, the] increased post-prandial metabolism may have promoted further reduction in fat mass and an increase in insulin sensitivity,” the researchers noted.

However, self-reporting may have influenced the findings. “[Nonetheless,] it is reassuring that the reported diet changes were paralleled by changes in weight and plasma lipid levels,” they pointed out. And while it appears that the study duration was sufficient for participants to adapt to the vegan diet regimen, its long-term effect should still be explored in future trials, they added.