Registered dietitian Brenna O'Malley, creator of the health blog The Wellful, said that we have an abundance of research showing us that diets "work" in the first few months, and it's also what many experience when starting a different diet plan. "That change in weight isn't what's being disputed," she said. "It's the sustainability of that loss, and the risk and side effects that come with it." Sure, the weight may come off if you eat 1,000 calorie a day, but O'Malley asked, at what cost to your mental and physical health will such restrictive dieting cause? You can't maintain a diet like that without causing harm.
Many diets and lifestyle plans aren't sustainable, one reason being that the restriction in calories leads to participants feeling out of control around food, because the body's physiological response to restricting is binge eating.
The diet may also be difficult to maintain if it doesn't fit in with their social or work lifestyle, if it limits their social engagements, or prevents them from being flexible, travelling, or having spontaneous plans. For example, if you're following a strict keto diet, you may be worried about not being able to eat or being tempted to "break your diet" if you go to a party or on a trip.
Another reason diets aren't sustainable is because they're not individualized to that person. O'Malley said, "We all have different food preferences, needs, lifestyles, health histories, and relationships with food, so it makes sense that there isn't one way of eating that would work for all of us."