medwireNews: The amount of weight loss achieved with a healthy low-fat (HLF) diet is no different to that achieved with a healthy low-carbohydrate (HLC) diet, according to US researchers.
Christopher Gardner and colleagues from Stanford University Medical School also found that weight change was not affected by genotypes predicting increased sensitivity to fat or carbohydrates, nor by insulin sensitivity.
These findings differ from previous studies suggesting that genotype or insulin-glucose dynamics can modify the response to specific diets. The researchers put this down to the higher nutritional quality of the diets they recommended, with both groups reducing or eliminating refined grains and added sugars while increasing vegetable intake.
For the Diet Intervention Examining The Factors Interacting with Treatment Success (DIETFITS) study, 609 participants aged 18 to 50 years, with a BMI between 28 and 40 kg/m2 and no history of diabetes were randomly assigned to follow a HLF (n=305) or HLC (n=304) diet for 12 months.
A total of 481 (79%) participants completed the study, at which point macronutrient distributions were 48%, 29%, and 21% for carbohydrates, fat, and protein, respectively, with the HLF diet, and 30%, 45%, and 23%, respectively, with the HLC diet.
Gardener and team report that, at 12 months, there was no significant difference in weight loss between the two groups, at 5.3 kg with the HLF diet and 6.0 kg with the HLC diet. The range for weight change (−30 kg to 10 kg) was also similar between the groups.
Both diets also led to improved lipid profiles and lowered blood pressure, insulin, and glucose levels. The only exception was an increase in low-density lipoprotein cholesterol concentrations for participants following the HLC diet.
Genotyping of single nucleotide polymorphisms in three genes (PPARG, ADRB2, and FABP2) linked to fat and carbohydrate metabolism suggested that 40% of participants were more sensitive to fat (low-fat genotype), while 30% were more sensitive to carbohydrates (low-carbohydrate genotype). The remainder were not sensitive to either.
However, neither genotype pattern nor baseline insulin secretion affected the amount of weight loss, and were therefore not helpful in identifying which diet was better for whom.
“The finding of no significant difference in weight loss in genotype-matched vs mismatched groups in the current study highlights the importance of conducting large, appropriately powered trials such as DIETFITS for validating early exploratory analyses,” Gardner et al write in JAMA.
They conclude: “[W]hen equal emphasis is given to high dietary quality for both low-fat and low-carbohydrate eating plans, it is not helpful to preferentially direct an individual with high insulin secretion status who is seeking weight loss to follow a lower-carbohydrate eating plan instead of a lower-fat eating plan.”
By Laura Cowen
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