Does A Whole Food Plant-Based Diet Work?

Carb-rich whole-grain bread

Depends on how you define “work.”

New Zealand researchers found significant long-term weight loss and improved cholesterol levels over six and 12 months with a low-fat vegetarian diet. Surprisingly, this was accomplished without restriction on calories and without an exercise component. Weight loss measured at six months was 27 lb (12.1 kg) and they only gained a little back by six months later.

The authors think the successful weight loss was from “… the reduction in the energy density of the food consumed (lower fat, higher water and fibre). Multiple intervention participants stated ‘not being hungry’ was important in enabling adherence.”

I scanned the article pretty quickly and don’t see that they referred to the diet as vegetarian. Here’s their test diet description:

We chose a low-fat iteration of the plant-based diet [7–15% if calories as fat] as this has been shown with previous research to achieve optimal outcomes, especially for heart disease and weight loss. This dietary approach included whole grains, legumes, vegetables and fruits. Participants were advised to eat until satiation. We placed no restriction on total energy intake. Participants were asked to not count calories. We provided a ‘traffic-light’ diet chart to participants outlining which foods to consume, limit or avoid. We encouraged starches such as potatoes, sweet potato, bread, cereals and pasta to satisfy the appetite. Participants were asked to avoid refined oils (e.g. olive or coconut oil) and animal products (meat, fish, eggs and dairy products). We discouraged high-fat plant foods such as nuts and avocados, and highly processed foods. We encouraged participants to minimise sugar, salt and caffeinated beverages.

Perfect diet compliance would make this a vegan diet. I didn’t catch it in the text of the article, but I’m guessing protein calories were 10–15% of the total, and carbohydrates were around 75%.

The researchers called their investigation the BROAD study. All study subjects were overweight or obese adults. A control group ate their regular foods. The intervention group eating the whole food plant-based diet numbered 33, including 7 with type 2 diabetes. All studies like this have people that drop out. I.e., they quit or otherwise get lost to follow-up. Of the intervention group, 75% lasted for six months, 70% stuck with it for the entire 12 months.

There weren’t enough diabetics in the study to make statistically significant conclusions, but the authors write, “Hemoglobin A1c reductions favoured the intervention and all intervention patients with a diabetes diagnosis improved while adherent, and two resolved their condition by HbA1c.”

I’d love to see these researchers repeat this study with 50–100 overweight or obese folks with T2 diabetes. Clearly, it’s a radically different diet than what I recommend for my patients with diabetes.

Steve Parker, M.D.

PS: For science nerds, here’s the study abstract:

Background/Objective: There is little randomised evidence using a whole food plant-based (WFPB) diet as intervention for elevated body mass index (BMI) or dyslipidaemia. We investigated the effectiveness of a community-based dietary programme. Primary end points: BMI and cholesterol at 6 months (subsequently extended).

Subjects: Ages 35–70, from one general practice in Gisborne, New Zealand. Diagnosed with obesity or overweight and at least one of type 2 diabetes, ischaemic heart disease, hypertension or hypercholesterolaemia. Of 65 subjects randomised (control n=32, intervention n=33), 49 (75.4%) completed the study to 6 months. Twenty-three (70%) intervention participants were followed up at 12 months.

Methods: All participants received normal care. Intervention participants attended facilitated meetings twice-weekly for 12 weeks, and followed a non-energy-restricted WFPB diet with vitamin B12 supplementation.

Results: At 6 months, mean BMI reduction was greater with the WFPB diet compared with normal care (4.4 vs 0.4, difference: 3.9 kg m−2 (95% confidence interval (CI)±1), P<0.0001). Mean cholesterol reduction was greater with the WFPB diet, but the difference was not significant compared with normal care (0.71 vs 0.26, difference: 0.45 mmol l−1 (95% CI±0.54), P=0.1), unless dropouts were excluded (difference: 0.56 mmol l−1 (95% CI±0.54), P=0.05). Twelve-month mean reductions for the WFPB diet group were 4.2 (±0.8) kg m−2 BMI points and 0.55 (±0.54, P=0.05) mmol l−1 total cholesterol. No serious harms were reported.

Conclusions: This programme led to significant improvements in BMI, cholesterol and other risk factors. To the best of our knowledge, this research has achieved greater weight loss at 6 and 12 months than any other trial that does not limit energy intake or mandate regular exercise.

Source: Nutrition & Diabetes – The BROAD study: A randomised controlled trial using a whole food plant-based diet in the community for obesity, ischaemic heart disease or diabetes