Interesting one year long study to compare low fat and “low-carb” diets points out the effect of individual variability on dietary results (Gardner CD, Trepanowski JF, Del Gobbo LC, Hauser ME, Rigdon J, Ioannidis JPA, Desai M King AC. 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. JAMA. 2018 Feb 20;319(7):667-679.). The study was a
…randomized clinical trial included 609 adults aged 18 to 50 years without diabetes with a body mass index between 28 and 40
The study looked at the two diets with respect to three categories:
The results were surprising (from my perspective).
…weight change over 12 months was not significantly different for participants in the HLF diet group (−5.3 kg) vs the HLC diet group (−6.0 kg),
there was no significant diet-genotype interaction
[there was no significant ] diet-insulin interaction
Genetic Distribution in this Study Population
This may be the most interesting result from this large population group. The distribution of low-fat and low-carb genotypes were 40% vs 30%.
- 244 [40%] had a low-fat genotype;
- 180 [30%] had a low-carbohydrate genotype
The genetic tests were for (Dieting With A New Twist — A Double Helix):
3 genes (PPARG, ADRB2, and FABP2) that are involved with fat and carbohydrate metabolism
Here is a critique of the genes that the study selected by the Genetic testing company (Arivale responds to DIETFITS study in Journal of American Medical Association (JAMA)).
The DIETFITS study considered three genetic variants in their analysis: FABP2 (rs1799883), PPARG (rs1801282), and ADRB2 (rs1042714). It is unclear why the investigators chose these specific genetic variants given that other variants also had evidence of gene/diet interaction at the time the study was designed.
Further, it appears that the investigators weighted each variant equally in their genetic model, regardless of the strength of the evidence or other factors. This may have affected the study outcomes, as which genetic variants are included in a genetic risk profile and how they are individually weighted is likely to play a role in what findings emerge.
Dietary Macronutrient Contents
This was not a ketogenic diet study by any stretch of the imagination.
In the HLF vs HLC diets, respectively, the mean 12-month macronutrient distributions were 48% vs 30% for carbohydrates, 29% vs 45% for fat, and 21% vs 23% for protein.
A well formulated ketogenic diet would have had 5% of calories from carbohydrates 20-30% from protein and the remainder 65-75% from fat.
[2018-06-20: Interesting commentary here – Registered Dietitian Health Educators: how fat do you want to get?].
Insulin sensitivity was done with an Oral Glucose Tolerance Test (Dieting With A New Twist — A Double Helix).
…the study participants were administered an oral glucose tolerance test*, and their patterns and amounts of insulin secreted in response to a 75-gram glucose challenge were determined — the 30-minute response was used as an indicator of carbohydrate sensitivity
Not a surprise that there was no correlation of insulin sensitivity levels and weight loss. This was due to the high level of the low-carbohydrate diet. Assuming 2,000 calories and 30% of calories from carbs would have been 600 calories from carbs or 150 grams from carbohydrates. This is too high of a level to be all that effective in dropping Insulin levels.
Insulin Sensitivity and Diet Type
Another study specifically looked at Insulin Sensitivity vs diet type (Cornier MA1, Donahoo WT, Pereira R, Gurevich I, Westergren R, Enerback S, Eckel PJ, Goalstone ML, Hill JO, Eckel RH, Draznin B. Insulin sensitivity determines the effectiveness of dietary macronutrient composition on weight loss in obese women. Obes Res. 2005 Apr;13(4):703-9.).
Obese nondiabetic insulin-sensitive (Si) (fasting insulin < 10 microU/mL; n = 12) and obese nondiabetic insulin-resistant (fasting insulin > 15 microU/mL; n = 9) women (23 to 53 years old) were randomized to either a high carbohydrate (CHO) (HC)/low fat (LF) (60% CHO, 20% fat) or low CHO (LC)/high fat (HF) (40% CHO, 40% fat) hypocaloric diet. Primary outcome measures after a 16-week dietary intervention were: changes in body weight (BW), Si, resting metabolic rate, and fasting lipids.
The results were interesting:
Insulin-sensitive (Si) women on the HC/LF diet lost 13.5 +/- 1.2% (p < 0.001) of their initial BW, whereas those on the LC/HF diet lost 6.8 +/- 1.2% (p < 0.001; p < 0.002 between the groups). In contrast, among the insulin-resistant women, those on the LC/HF diet lost 13.4 +/- 1.3% (p < 0.001) of their initial BW as compared with 8.5 +/- 1.4% (p < 0.001) lost by those on the HC/LF diet (p < 0.04 between two groups).
The state of Si determines the effectiveness of macronutrient composition of hypocaloric diets in obese women. For maximal benefit, the macronutrient composition of a hypocaloric diet may need to be adjusted to correspond to the state of Si.