No Difference in Weight Loss Outcomes With Low-Fat vs Low-Carbohydrate Diet

A family eating dinner together
A family eating dinner together
There was no significant difference in 12-month weight loss between the healthy low-fat and low-carbohydrate diets, and neither genotype pattern nor baseline insulin secretion was associated with the dietary effects on weight loss.

Individuals placed on a healthy low-fat or healthy low-carbohydrate diet may not experience a difference in weight reduction between the 2 diets, and genotype patterns and baseline insulin secretion may not be associated with dietary effects on weight loss, according to a study published in JAMA.

Researchers conducted a prospective, single-site, parallel-group, weight loss diet trial (DIETFITS; identifier: NCT01826591), randomly assigning 609 individuals to be placed on either a low-fat (n=305) or low-carbohydrate (n=304) diet for 12 months with a primary outcome of determining weight loss between the 2 diet groups. Individuals received 22 instructional sessions over the course of 12 months, led by dieticians in diet-specific groups.

Also assessed during the study was whether a set of 3 single-nucleotide polymorphism (SNP) genotype patterns or baseline differences in insulin secretion were factors that predispose an individual to differential success in weight change over the course of 12 months when placed on either a low-fat or low-carbohydrate diet. Data were collected at months 3, 6, and 12 for both dietary cohorts.

Of the 481 individuals who completed the study (79%), 130 (42.6%) in the low-fat group had the low-fat genotype, and 83 (27.2%) had the low-carbohydrate genotype. In the low-carbohydrate group, 114 (37.5%) had the low-fat genotype and 97% (31.9%) had the low-carbohydrate genotype.

Study results found a weight decrease for those in the low-fat and low-carbohydrate groups to be −5.3 kg (95% CI, −5.9 to −4.7 kg) and −6.0 kg (95% CI, −6.6 to −5.4 kg), respectively, but these results were not found to have a statistically significant difference. There were also no statistically significant differences among diet and genotype pattern at the end of the 12-month study, as the study found there was no difference in weight change for individuals who were matched or not matched according to the diet assignment based on their 3 SNP genotype pattern (P =.20). In addition, there was no statistically significant correlation between baseline insulin secretion (blood concentration of insulin 30 minutes after a glucose challenge) and the 12-month study period (P =.47).

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In regard to secondary outcomes studied, there were no significant differences between groups for body mass index, body fat percentage, or waist circumference. Low-density lipoproteins were found to have decreased in the low-fat group and increased in the low-carbohydrate group. High-density lipoproteins increased and triglycerides decreased more significantly for those in the low-carbohydrate vs low-fat diet group. Resting energy expenditure was found to decrease from baseline in both groups, with no significant differences observed between groups at 6 and 12 months.

There were 7 serious adverse events reported, with 2 possibly related to the study, and there were also 11 adverse events, with 9 likely related or possibly to the study. Combined adverse events were evenly distributed between both diet groups.

Researchers concluded that there were no significant differences in weight loss between individuals placed on a low-fat or low-carbohydrate diet. In addition, genotype patterns and baseline insulin secretion were not found to be significantly associated with dietary effects on weight loss during the 12-month study. Therefore, clinicians should not consider genotype patterns or baseline insulin secretion as significant predictors of weight loss success when recommending individuals be placed on either a low-fat or low-carbohydrate diet.


Gardner CD, Trepanowski JF, Del Gobbo LC, et al. 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;319:667-679.