Just Read: In a Study of Body Fat Loss and Carbohydrate Restriction vs Fat Restriction – a look at the lipid changes caught my eye the most

This is a paper comparing the fat burning capability of either a low carbohydrate or low fat diet among 19 adults confined to a metabolic ward (very controlled conditions). The authors conclude that amount of body fat loss (but not weight) is greater in the low fat eating subjects, supporting the “calorie in/calorie out” hypothesis.

What I was struck by, though is the lipid changes that were seen in the subjects.

The authors of this paper have traded correspondence with other scientists in the low-carbohydrate community about the methods and validity of this approach (citations at the bottom of this post). Specifically, some points of controversy are

  • Using isocaloric diets to compare the two approaches. As Tim Noakes (@ProfTimNoakes) points out in his very detailed analyses (see: Just Read: Tim Noakes and Marika Sboros – Lore of Nutrition: Challenging Conventional Dietary Beliefs), in a real world situation, this would result in a person on a low carb diet eating more than they wanted to because this diet is more satiating than a high carbohydrate one. Often, as it is pointed out, studies tell low carb subjects to eat until they are full, the high carb subjects’ caloric intake is controlled – this in an of itself says something.
  • The timeframe of comparison. The intervention diets were eaten for 6 days, far less than would be expected for fat adaptation (I’m aware of the debate about this between David Ludwig, MD, and the authors, see citations at the bottom of this post)

Lipids

What I immediately noticed is the impact on lipid proportions

  • Significant triglyceride drop in the low carbohydrate group, no change in the low fat (high carbohydrate) group
  • Small HDL drop in the low carbohydrate group, bigger drop in the low fat (high carbohydrate) group
  • Total Cholesterol and LDL went down more in the low fat group relative to the low carboydrate group

These changes are predicted with these diets. When I calculated the TG/HDL ratios based on the averages (I don’t have the raw data), they were:

  • 1.98 TG/HDL for the low carbohydrate group
  • 2.58 TG/HDL for the low fat group

& trended the wrong (unhealthy) way for the low fat group compared to the low carbohydrate group. For more about why this is the unhealthy direction, see: Just Read: Challenging the role of LDL vs Insulin Resistance in predicting heart disease, via Kaiser Permanente data

Other metabolic changes

Also as predicted from a dietary pattern like this, the low carbohydrate subjects’ insulin levels dropped, as well as their insulin resistance. The high carbohydrate subjects’ insulin levels remained the same, with their insulin resistance dropping as well. It looks to me like on average there was early insulin resistance among the subjects at baseline, which should be concerning.

My questions

The authors state

Fat loss is a more important goal than weight loss in the treatment of obesity.

and

While the fat balance method does not determine the anatomical location of lost fat, decreased adipose tissue triglyceride likely makes up the majority. Any additional loss of ectopic fat from liver or skeletal muscle would likely be even more beneficial.

  1. If metabolic markers are showing a tendency to diabetes in the low-fat (high carbohydrate group), might this be a bigger health threat than fat loss?
  2. What would the trajectory of insulin resistance be over a long period of time if these trends continue?
  3. Wouldn’t it be likely with this lipid pattern that more fat would be deposited in the liver, exacerbating non-alcoholic fatty liver disease?

A few more notes

  • The authors take author Gary Taubes’ to task in their introduction which says something about how they approach this topic
  • They imply that the increase fat mass loss (but not weight loss, which was higher in the low carbohydrate group) may be due to muscle wasting, and mention the same 4 studies from 1969 to 1995, however this doesn’t seem consistent with other studies I’ve seen.

I am not the expert here (and still catching up), so follow-up studies and commentaries can be found in these places, including twitter (thank you social media):

  1. Hall KD, Bemis T, Brychta R, Chen KY, Courville A, Crayner EJ, et al. Calorie for calorie, dietary fat restriction results in more body fat loss than carbohydrate restriction in people with obesity. Cell Metab [Internet]. 2015;22(3). Available from: http://dx.doi.org/10.1016/j.cmet.2015.07.021
  2. Roberts SB, Das SK. One Strike against Low-Carbohydrate Diets. Cell Metab [Internet]. 2015 Sep;22(3):357–8. Available from: http://linkinghub.elsevier.com/retrieve/pii/S1550413115003514
  3. Ludwig DS, Ebbeling CB. Raising the bar on the low-carbohydrate diet. Am J Clin Nutr [Internet]. American Society for Nutrition; 2016 Nov 1 [cited 2017 Dec 17];104(5):1487–8. Available from: http://www.ncbi.nlm.nih.gov/pubmed/27802995
  4. Hall KD, Chen KY, Guo J, Leibel RL, Mayer LE, Reitman ML, et al. Reply to DS Ludwig and CB Ebbeling. Am J Clin Nutr [Internet]. American Society for Nutrition; 2016 Nov 1 [cited 2017 Dec 17];104(5):1488–90. Available from: http://www.ncbi.nlm.nih.gov/pubmed/27802997
  5. Hall KD, Chen KY, Guo J, Lam YY, Leibel RL, Mayer LE, et al. Energy expenditure and body composition changes after an isocaloric ketogenic diet in overweight and obese men. Am J Clin Nutr [Internet]. American Society for Nutrition; 2016 Aug 1 [cited 2017 Dec 17];104(2):324–33. Available from: http://www.ncbi.nlm.nih.gov/pubmed/27385608

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