While there are many debates about which type of diet is best for weight loss and health, it's often not the weight loss which is the biggest challenge, but rather avoiding weight regain afterwards.
But recently, "reverse dieting" has gained popularity online as a post-diet eating plan that claims it can help you avoid weight regain by eating more. In simple terms, it's a controlled and gradual way of increasing from a low calorie weight-loss eating plan back to your more "normal" pre-diet way of eating.
The idea with reverse dieting is that gradually increasing calorie intake following a deficit will allow your body and your metabolism to "adjust" so that you can avoid weight regain while eating more.
However, there is currently no scientific evidence showing that reverse dieting works as advocates claim.
Reverse dieting is based around the theory that our body has baseline "set points" for metabolism and calorie intake hardwired into our biology, and if we go above these points we gain weight.
The idea is that reverse dieting can shift these "set points" upwards if a person slowly increases the amount of calories eaten as food. This would theoretically "boost" their metabolism, allowing them to consume more food and calories without gaining weight.
However, the idea that as humans we have a "set point", which we can manipulate with dietary changes, is not supported by research.
The main reason for this is because a number of factors influence our weight and metabolism, including how it changes. Among them are how we're brought up, what food we have access to, what type of exercise we do, and our genetics.
But the most important influence over how our body uses calories – and therefore our weight – is our resting (or basal) metabolic rate. This is the amount of calories our body needs in order to keep itself alive. This accounts for about 60 to 70 percent of the calories we use daily.
Our basal metabolic rate is mostly determined by our age, weight, sex and muscle mass – your diet has little effect on it.
Eating at or below your basal metabolic rate will result in weight loss, and eating above it will result in weight gain.
Our basal metabolic rate also increases as we gain weight or muscle mass, and decreases as we lose weight or muscle mass (the evidence shows that the more muscle your body has, the more calories it needs to function).
Exercise also increases how many calories we use, but usually not enough to massively affect our weight. And though a high protein diet can alter metabolic rate somewhat, our body weight and muscle mass have the greatest effect on it.
So reverse dieting only appears to work by controlling calorie intake. There's currently no evidence that you can alter your metabolism or metabolic rate by introducing more calories slowly and gradually.
Put simply, if you eat more calories than your body requires, you will gain weight. What we do know is that certain habits, like regularly eating breakfast and exercise, help people avoid weight regain after dieting.
While there's currently little research investigating the effects of reverse dieting on metabolism, it could still help people in other ways.
When some people are losing weight, they may feel in control of how they eat. But for some people, stopping their diet could lead to perceived loss of control.
Reverse dieting might give some people the confidence to return to a more sustainable way of eating, or help them move out of a cycle of restrictive dieting.
Advocates of reverse dieting suggest it can also help manage problems of appetite and cravings. This is because additional foods can be added in as the amount of calories and food eaten is increased.
While fewer cravings can help with weight maintenance, this evidence does not come from studies where foods were slowly reintroduced.
For some people, counting calories or restrictive dieting can tend to lead to an unhealthy relationship with their bodies and the food they eat.
Orthorexia nervosa is becoming increasingly common, and is characterised by an obsession with eating healthy – which can lead to an unhealthy restriction of and relationship with foods.
While wanting to eat a healthy diet can seem on the surface to be a good thing, when it becomes orthorexia and enjoyment of food is replaced by an anxiety of feeling the need to account for every calorie, this could lead to poor mental health.
Reverse dieting is one approach, but some would argue other methods, such as intuitive eating – which emphasises listening to your body's hunger cues and only eating when you're hungry – might be psychologically healthier. Intuitive eating may help people both regain and trust their appetites, and stop the cycle of restriction and calorie counting.