Study provides some answers to ongoing debate about which diet causes most weight loss.
Most diet trials have reported modest mean weight loss after 12 months and negligible mean weight loss differences between diet groups. Prior studies have suggested that some strategies may work better for some individuals than others, and that no one diet should be recommended universally, but inter-individual differences in response to diet are still poorly understood. Some studies have reported that genotype variation could predispose individuals to differential weight loss that varies by diet type. Other studies have reported that baseline insulin dynamics may explain differential weight loss success obtained via a low-fat diet vs a low-carbohydrate diet. For example, individuals with greater insulin resistance may have better success with low-carbohydrate diets due to the decreased demand on insulin to clear a lower amount of dietary carbohydrate delivered to the circulation. However, these studies are still limited and further insight regarding this perspective is needed.
In a multicenter randomized trial to determine the effects of diets varying in carbohydrate-to-fat ratio on total energy expenditure, participants were randomly assigned to one of three test diets according to carbohydrate content (high, moderate, or low) for 20 weeks. Test diets were controlled for protein and were energy adjusted to maintain weight loss within 2 kg.
The study found that total energy expenditure was significantly greater in participants assigned to a low carbohydrate diet compared with a high carbohydrate diet of similar protein content with a linear trend of 52 kcal/d for every 10% decrease in the contribution of carbohydrate to total energy intake. In addition, they found that pre-weight loss insulin secretion might modify individual response to this diet effect.
The study concluded that consistent with the carbohydrate-insulin model, lowering dietary carbohydrate increased energy expenditure during weight loss maintenance. This metabolic effect may improve the success of obesity treatment, especially among those with high insulin secretion.
Another recent randomized clinical trial that included 609 adults age 18 to 50 years without diabetes, with a body mass index between 28 and 40, aimed to determine the effect of a healthy low-fat diet vs a healthy low-carbohydrate diet on weight change and if genotype pattern or insulin secretion are related to the dietary effects on weight loss.
The primary outcome measure was a 12-month weight change and determination of whether there were significant interactions among diet type and genotype pattern, diet and insulin secretion, and diet and weight loss. Weight change at 12 months was -5.3 kg for the healthy low fat diet vs -6.0 kg for the healthy low carbohydrate diet.
The study concluded that in this 12-month weight loss diet study, there was no significant difference in weight change between a healthy low-fat diet vs a healthy low-carbohydrate diet, and neither genotype pattern nor baseline insulin secretion was associated with the dietary effects on weight loss. In the context of these 2-common weight loss diet approaches, neither of the two hypothesized predisposing factors was helpful in identifying which diet was better for whom.
According to an article in AARP, one of the authors of this new study, Christopher Gardner, states that the findings of this study don’t contradict the low carb study by CB Ebbeling et al, but suggest there may be some flexibility in the ways we can lose weight, stating that limiting processed foods could improve most diets by cutting down overall calories, while still leaving room for people’s preferences; and for diet to be effective, a person must be able to stick to it.
Therefore, large randomized trials that are appropriately powered are required to further look into factors that may influence the effect of diet on certain individuals more than others.
For the meanwhile, as stated in an interview with Zhaoping Li, director of the clinical nutrition division at the University of California, “there is no single set of guidelines that help everyone lose weight and keep it off” and what Li tries to do with her patients is examine their eating and physical activity routines to identify improvements people will be able to live with.
- Both low carb diets and low fat diets have been found to be effective for weight loss and there is no set of guidelines to recommend one or another.
- Genotype patterns and insulin secretion have been found to be related to dietary effects on weight loss in previous small trials but have still yet to be confirmed in large randomized trials.
- Large randomized trials that are appropriately powered are required to further look into factors that may influence the effect of diet on certain individuals more than others.
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.
Ebbeling CB, Feldman HA, Klein GL, Wong JMW, Bielak L, Steltz SK, Luoto PK,Wolfe RR, Wong WW, Ludwig DS. Effects of a low carbohydrate diet on energy expenditure during weight loss maintenance: randomized trial. BMJ. 2018 Nov 14;363:k4583.
Dahlia Elimairi, Pharm D Student, UC Denver Skaggs School of Pharmacy