Is there a “best diet” for fat loss?

Usually, in diet studies, weight loss differs little between diet groups but a lot within each group. In other words, individual results will vary. For example, in the Diet Intervention Examining The Factors Interacting with Treatment Success (DIETFITS) RCT, 600 participants were randomly assigned to either a low-fat or low-carb (non-keto) diet for 1 year, with intensive support from dietitians and research staff.^[1]

Here were the reported weight-loss averages:

• 5.3 kg (11.7 lb) in the low-fat group
• 6.0 kg (13.2 lb) in the low-carb group As you can see in the figure below, in which each bar represents the weight change of a single participant, individual changes varied widely in both groups: they ranged from -32 to +11 kg (-70 to +24 lb).

Adapted from Gardner et al. JAMA. 2018.^[1]

One reason for these differences is that some people stick to their diets while others don’t (a support network is very helpful for diet adherence), but another may be that some diets do work better for some people than for others, for reasons that aren’t yet completely understood.

If there’s one takeaway to keep in mind after looking at all the evidence, it is that no one diet is inherently superior. Different diets work differently for different people, but the best fat-loss diet for a specific person will have at least two qualities: it’ll be hypocaloric (it’ll make adherents eat less than they burn) and sustainable (it’ll fit food preferences and lifestyle well enough that adherence is possible).