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Effects of a low carbohydrate diet on energy expenditure during weight loss maintenance: randomized trial

BMJ 2018; 363 doi: https://doi.org/10.1136/bmj.k4583 (Published 14 November 2018) Cite this as: BMJ 2018;363:k4583

Rapid Response:

Let's give diets based on whole foods the benefit of the doubt

The details of the diet given in the methods paper:

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6163108/

make it clear that while this study has stuck to the official guidelines and recommendations for nutrient composition, there is still a problem here that should be addressed by all researchers in this field. According to the article:

"Total fiber content was consistent with recommendations from the Institute of Medicine (1) and reflected a gradient across the 3 diets (17.5, 15, and 12.5 g/1000 kcal with the high-, moderate-, and low-carbohydrate diets)."

Now, the argument for a low-fat high carb diet has its roots in observational studies done on indigenous populations, e.g. (2), but the sorts of diets that people in such studies ate, are planted based whole food diets containing small amounts of meat and fish that are very low in refined oils. Such diets have a fiber content of a factor of 2 to 3 higher than the current recommendation. Also such diets will contain much more magnesium, which is an element that plays an important role in metabolism, also about a factor of 2 to 3 more than current guidelines.

We can easily verify this by considering the fiber and magnesium contents of a list of whole foods and computing the amounts of these nutrients per Kcal of energy. E.g. potatoes contain 2.9 *10^(-2) g/Kcal of fiber and 0.3 mg/Kcal of magnesium. Looking at a large list of many such energy rich whole foods reveals that a 2500 Kcal carb based whole food diet should contain at least 0.7 grams of magnesium and at least 70 grams of fiber. Here we note that sources of dietary fat cannot be refined oils but can be foods like walnuts, almonds, linseed etc. which are also high in magnesium and fiber. Also vegetables have a much higher fiber to energy ratio than then carb-rich foods.

One can formulate this in the opposite way by asking what kind of whole food diet of a 2500 kcal would actually yield the RDAs of 400 mg of magnesium and 40 grams of fiber. One then finds that this is not possible, unless one includes large amounts of olives which contain an atypically low amount of fiber and magnesium per unit energy.

Then given that the human body should be assumed to have adapted itself to a diet that based on unrefined foods that can be obtained from Nature, we should have some doubts about the healthfulness of the much lower official recommendations for fiber and magnesium compared to that of a diet based on whole foods.

1. Institute of Medicine Dietary Reference Intakes for energy, carbohydrate, fiber, fat, fatty acids, cholesterol, protein, and amino acids. Washington (DC): National Academies Press; 2002.

2. Shaper AG, Jones KW. Serum-cholesterol, diet, and coronary heart-disease in Africans and Asians in Uganda. The Lancet, 534–537 (1959).

Competing interests: No competing interests

21 November 2018
Saibal Mitra
Consultant
The Netherlands