Head to head, the diets tie
Compared to no diet, low-carb diets produced about 8.7 kg at six months and low-fat about 8.0 kg. Differences between named diets were small: Atkins beat Zone by 1.7 kg at six months. The authors' own conclusion was that this supports recommending any diet a person will stick to.
A year of healthy low-fat versus healthy low-carb: 5.3 vs 6.0 kg lost, a difference that wasn't significant. Neither genetic testing nor insulin response predicted who did better on which diet.
Why most diets fail
All four diets lost roughly 2–3 kg over a year. Only half to two-thirds of people finished. The key finding: weight loss tracked how closely people followed their diet (a strong correlation), and had almost nothing to do with which diet it was.
Diets rarely fail because the plan was wrong. They fail because the plan was too hard to keep doing.
Strict or flexible?
People who controlled their eating rigidly (all-or-nothing rules, forbidden foods) had more binge eating and higher body weight. People with flexible control (moderating amounts, compensating later) had lower body weight, fewer binges, and were more likely to succeed in a one-year programme.
Mostly adults with overweight or obesity who weren't lifting. Johnston, Gardner and Dansinger are randomised trials. Westenhoefer is observational: it shows that flexible eaters do better, not that switching to flexible eating will cause better results. It fits with what I see coaching, but it isn't proof.
What to do
- Pick the eating style you can see yourself doing in a year, not the one with the best marketing.
- Keep the non-negotiables: a calorie deficit and enough protein. Everything else is preference.
- Drop the forbidden-foods list. Plan for treats in reasonable amounts instead.
- One off-plan meal is a meal, not a failure. Get back on at the next one.
- If you keep breaking the plan, the plan is too strict. Change it.
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