Yo-yo dieting: why the weight comes back and how to stop it

You lost the weight, celebrated, and a few months later the kilos are back. Sometimes with interest. This is called yo-yo dieting, and you are not alone in it. In most cases the cause is a badly set up process, and willpower has little to do with it. A process can be changed.

Short answer: Yo-yo dieting comes from a badly set up process: too big a deficit, muscle loss, and a diet with a fixed end date. Willpower is rarely the reason. To make results last, keep a mild deficit of 15 to 20% below your energy use, eat 1.6 to 2 g of protein per kg, lift weights, and after the diet add calories back step by step up to maintenance.

Why yo-yo dieting happens

Most yo-yo stories follow the same script. A hard diet, fast loss, a return to old habits, and the kilos are back. Usually several things come together: a deficit that is too big, muscle loss, and a diet with a clear 'end' instead of habits that change for good.

Muscle loss means a slower metabolism

When you lose weight aggressively and without protein and strength training, your body doesn't take only fat. It takes muscle too. And muscle burns energy even at rest, when you just lie on the couch. Less muscle means lower daily energy use, so fat comes back more easily once you return to normal food.

Head and habits decide

"I'll diet for a month and then eat normally again." Look at the word "normally". If you go back to exactly what led to the extra weight, you get the same result. A diet with an end date does not work. A gradual change in habits that you can still keep in a year does.

How to lose weight so it lasts

• A mild deficit (15 to 20% below your energy use), not starvation.
• Enough protein (1.6 to 2 g per kg): it protects muscle and keeps you full.
• Strength training: it gives your body a reason to keep its muscle.
• Gradual changes instead of a big change overnight. A flexible way of eating helps here, see flexible dieting.
• Follow the trend over weeks, not the day-to-day swings on the scale. More in why your weight fluctuates.

What your body does for a year after a diet

When you reach your goal weight, your body doesn't accept it from one day to the next. Sumithran et al. (2011, PMID 22029981) measured this in 50 people: appetite hormones had not returned to normal even a year after the diet. Appetite stayed in a different place than before the weight loss. That is why after a hard diet you feel pulled back. It is not your fault. Your body keeps the setting from the time you were losing weight. Hormones drive hunger after a diet, and for most people you can't switch that off with willpower overnight.

The second study is a different league. Fothergill et al. (2016, PMID 27136388) followed 14 participants of an extreme weight loss competition for six years. Their resting metabolism stayed about 700 kcal (calories) a day lower. That is an extreme case, not normal weight loss. With clients on a mild deficit I see a different course: the head wants to eat like before, and the body reports hunger for longer than you expect. The more you overdo the diet, the more your body defends the old weight. That is why in coaching we go slowly, with muscle and a return to maintenance. The body needs time.

After the diet: the most important and most neglected part

When you reach your goal, don't jump back to eating the old way. Add calories back to your maintenance intake step by step, and stay at that level for a while. You teach your body and your head to live with the weight you worked for. This is exactly the difference between "back again" and "it holds".

Fat loss is a change you can live with, not a one-month sprint. Set it up sensibly and yo-yo dieting has nothing to hold on to. The weekend is often where a plan cracks, so see weekend overeating too.

Frequently asked questions

Why does metabolism slow down after aggressive weight loss?

When you lose weight aggressively and without protein and strength training, your body takes muscle as well as fat. Less muscle means lower daily energy use, so fat comes back more easily once you return to normal food.

How big a calorie deficit should I keep so the weight does not come back?

A mild one: 15 to 20% below your energy use, no starvation. Add enough protein (1.6 to 2 g per kg) and strength training, which gives your body a reason to keep its muscle.

Why am I still hungry after a diet?

Sumithran et al. (2011) measured in 50 people that appetite hormones had not returned to normal even a year after the diet. Your body keeps the setting from the time you were losing weight, and for most people you can't switch that off with willpower overnight.

How do I go back to normal eating after a diet?

Don't jump back to the old way of eating. Add calories back to your maintenance intake step by step, and stay at that level for a while.

Why doesn't "a diet for a month and then normal food" work?

If you return to exactly what led to the extra weight, you get the same result. What works is a gradual change in habits that you can keep for a year or longer.

Sources, so you can check:

1) Appetite hormones after weight loss: Sumithran P, Prendergast LA, Delbridge E, Purcell K, Shulkes A, Kriketos A, Proietto J. Long-term persistence of hormonal adaptations to weight loss. N Engl J Med. 2011;365(17):1597-1604. DOI: 10.1056/NEJMoa1105816 | PMID: 22029981

2) Metabolism after extreme weight loss: Fothergill E, Guo J, Howard L, et al. Persistent metabolic adaptation 6 years after "The Biggest Loser" competition. Obesity (Silver Spring). 2016;24(8):1612-1619. DOI: 10.1002/oby.21538 | PMID: 27136388

Martin Barna

Online nutrition and fitness coach. Since 2013 I have helped 600+ people lose fat and keep the result. Science, not crash diets.

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This article is for information only. It is not medical advice. If you have a health condition, talk to your doctor.