Overweight or obese and wanting to lose weight?  Which diet would be best to follow – a low-fat or low-carbohydrate diet?   If you have a genetic predisposition to do better on one of these diets, what difference would it make?  What role does your level of insulin secretion play in your efforts to lose weight?

A comprehensive study conducted by researchers from the Stanford Prevention Research Centre has tried to answer these questions – whether low-fat or low-carb diets are more effective for some people, based on their genetic makeup and insulin secretion levels..  The results are unexpected!

A total number of 609 overweight or obese men and woman between the ages of 18 and 50 participated in this 12 month long study, called DIETFITS (Diet Intervention Examining The Factors Interacting with Treatment Success).  Testing for three genetic variants were used to determine which of the participants had a predisposition to react better to a low-fat or a low-carb diet. Their levels of insulin sensitivity, which plays a role in the metabolism of food, were also tested. (Being overweight increases insulin secretion, and other studies have suggested that having a higher insulin level may make it harder to lose weight).

The participants in the study were then randomly selected into two groups to follow either a healthy low-carb diet or a healthy low-fat diet.  For the first two months the fat or carb intake were limited to extremely low levels, and then gradually increased to levels they felt they could maintain for life.  During the course of the study everybody participated in 22 small-group sessions with registered dietitians, advising them on a behavioural weight loss approach and healthy diet.  In terms of diet, all participants were instructed to eat lots of vegetables, to choose high-quality nutritious whole foods, to limit processed foods, to prepare food themselves, and to avoid trans-fats; added sugars; and refined carbohydrates. They also had access to counsellors for personal guidance, motivation and advice.  Participants were encouraged to follow an exercise programme, consisting of moderate intensity physical activity for at least two and a half hours per week.

At the end of the trial period full measurements were again taken of the 481 participants who completed the study.  The effects of the individual’s genetic predisposition towards a low-carb or low-fat diet, as well as their level of insulin sensitivity were found to be insignificant in terms of weight loss.  The difference in weight loss between the healthy low-carb (average weight loss 6 kg) or the healthy low-fat diets (average weight loss 5,3 kg) the two groups of participants had followed, was also not significant. There were, however, variations in the amount of weight that individuals lost.  The results highlight that neither the genetic predisposition nor insulin sensitivity was helpful in identifying which diet was best for whom.

Although participants were not give guidelines on lowering calories, the more healthy diets resulted in participants on average reducing their calorie intake by 500 – 600 calories per day.

What the study did highlight was the value of a sustainable and healthy lifestyle change, in terms of diet and physical activity.  Harvard Medical School reviewed the study and concluded: “The best diet is the one we can maintain for life and is only one piece of a healthy lifestyle.  People should aim to eat high-quality, nutritious whole foods, mostly plants (fruits and veggies), and avoid flours, sugars, trans fats, and processed foods (anything in a box).  Everyone should try to be physically active., aiming for about two and a half hours of vigorous activity per week.  For many people, a healthy lifestyle also means better stress management, and perhaps even therapy to address emotional issues that can lead to unhealthy eating patterns.”

(Please see Health Insight’s program for intensive lifestyle change on www.healthinsight.co.za)



Effect of low-fat vs low-carbohydrate diet on 12-month weight loss in overweight adults and the association with genotype pattern or insulin secretion: The DIETFITS randomized clinical trial. Gardner CD et al. Study abstract published 20 February 2018 in JAMA. (Journal of American Medical Association.)

Which diet is best for long-term weight loss? Published online 9 April 2018. Harvard Medical School.

DIETFITS Study (Diet Intervention Examining The Factors Interacting with Treatment Success). Published in Clinical Trials, National Institutes of Health. U S National Library of Medicine.

DIETFITS Study (Diet Intervention Examining The Factors Interacting with Treatment Success) – Study design and methods. Published in Contemporary Clinical Trial. Volume 53, February 2017. Science Direct.

Genetics: still a factor for weight loss. Arivale responds to DIETFITS study in Journal of American Medical Association (JAMA). Published 2 March 2018 by Arivale. The scientific approach to wellness. (www.arivale.com)



June 2018






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