Even with lots of coaching, people can’t stick perfectly to diets that require them to eat a lot more protein or less fat—most end up eating closer to their old habits, but still lose weight.

Even though people were told exactly what percentage of fat, protein, and carbs to eat for two years — and got lots of help — they didn’t stick to it well, and everyone lost about the same amount of weight anyway. This means it’s hard to follow strict diet rules long-term.