According to the World Health Organisation, most people live in countries where overweight and obesity causes more deaths than being underweight. In 2016, 39% of adults aged 18 years and over were overweight, and 13% were obese.
The impact of being overweight or obese on health is significant. Having a raised body mass index (BMI) is a major risk factor for:
- cardiovascular diseases (mainly heart disease and stroke)
- musculoskeletal disorders (especially osteoarthritis)
- some cancers (including endometrial, breast, ovarian, prostate, liver, gallbladder, kidney, and colon)
The Centers for Disease Prevention (CDC) highlight that obesity is associated with poorer mental health outcomes and reduced quality of life. Researchers highlight that there is an urgent need for dietary interventions to address these problems. There is also a need for a better understanding of how different dietary interventions work.
With this information in mind, scientists from the Physicians Committee for Responsible Medicine (a non-profit of 12,000 doctors) decided to answer the question, “What are the effects of a low-fat vegan diet on body weight, insulin resistance, postprandial metabolism, and intramyocellular and hepatocellular lipid levels in overweight adults?”
Published in JAMA Network Open, scientists carried out a randomized control trial where overweight participants with no history of diabetes were assigned to an intervention or control group for 16 weeks. Participants in the intervention group followed a low-fat, plant-based diet. People assigned to the control group made no diet changes. The participants self-reported what they ate during the 16-week trial.
244 participants took part in the study conducted between January 2017 and February 2019 in Washington, DC. 122 people were randomly assigned to the intervention group, and 122 to the control group. Participants ranged in age from 25 to 75 years, and their BMI ranged from 28 to 40. The intervention group also attended weekly classes on dietary information led by health professionals. All of the participants were advised to continue their regular exercise habits.
Results from this randomized clinical trial showed that a low-fat plant-based dietary intervention reduces body weight by reducing energy intake and increasing postprandial (post mealtime) metabolism. Researchers identified that the plant-based diet increased after-meal calorie burn (postprandial metabolism) by 18.7%, on average, for the intervention group over the control. This is owing to increased insulin sensitivity resulting from reduced hepatocellular and intramyocellular fat (lipids in muscle and liver cells).
The research team advised that the plant-based diet’s effect on weight and insulin action are clinically important, highlighting that this intervention may be an effective treatment for overweight adults.
Following the original trial, a second analysis then took place. Researchers decided to ascertain whether the plant-based dietary intervention’s effects on body weight, blood lipid concentrations, and glycemic control were associated with blood type.
Published in the Journal of the Academy of Nutrition and Dietetics, results showed that blood type is not associated with the effect of a plant-based diet on body weight, body fat, plasma lipid concentrations, or glycemic control. This debunks the “blood type diet,” which recommends a mainly plant-based diet for those with blood type A – but a diet heavy in meat for people with blood type O.
The results showed that dietary changes, especially increased intake of fruits, vegetables, and grains, are beneficial not only to individuals with blood type A but also to all individuals regardless of blood type. They advise that there is no apparent value in limiting these healthy diet changes to a specific set of individuals based on blood group.
Written by Helen Massy, BSc.
Barnard, N., Rembert, E., Freeman, A., Bradshaw, M., Holubkov, R. and Kahleova, H., 2020. Blood Type Is Not Associated with Changes in Cardiometabolic Outcomes in Response to a Plant-Based Dietary Intervention. Journal of the Academy of Nutrition and Dietetics,.
Centers for Disease Control and Prevention. 2020. Adult Obesity. [online] Available at: <https://www.cdc.gov/obesity/adult/causes.html> [Accessed 16 December 2020].
Kahleova, H., Petersen, K., Shulman, G., Alwarith, J., Rembert, E., Tura, A., Hill, M., Holubkov, R. and Barnard, N., 2020. Effect of a Low-Fat Vegan Diet on Body Weight, Insulin Sensitivity, Postprandial Metabolism, and Intramyocellular and Hepatocellular Lipid Levels in Overweight Adults. JAMA Network Open, 3(11), p.e2025454. Who.int. 2020. Obesity And Overweight. [online] Available at: <https://www.who.int/news-room/fact-sheets/detail/obesity-and-overweight#:~:text=In%202016%2C%20more%20than%201.9,kills%20more%20people%20than%20underweight.> [Accessed 16 December 2020].
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