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. Often 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 often 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 2.2 g of protein per kg of body weight (if you have a lot to lose, use your goal weight), lift weights, and after the diet add calories back step by step up to maintenance.
Why yo-yo dieting happens
With clients, I see the same script again and again. 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.
Why metabolism slows down after a diet
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 somewhat lower daily energy use. On top of that, a smaller body simply burns less, and for a while your body also saves some energy on its own. The muscle part is smaller than people think, but it adds up with the rest, which is why protein and strength training matter.
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 usually ends with the old habits back. What I see working with clients is a gradual change you can still keep in a year.
How to lose weight so it lasts
- A mild deficit (15 to 20% below your energy use), not starvation.
- Enough protein (1.6 to 2.2 g per kg of body weight, or of your goal weight if you have a lot to lose): 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) put 50 people with overweight or obesity on a 10-week very-low-calorie diet. A year later, in those who completed the study, several appetite hormones and hunger had still not returned to their pre-diet levels. 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. After a diet, hormones push your hunger up. That doesn't switch off energy balance, but it makes it harder to hold, and willpower alone rarely beats it overnight.
If dieting has turned into cycles of restricting and bingeing, or food causes you a lot of stress, talk to your doctor or an eating disorder specialist. If you feel overwhelmed, contact a local crisis line (in the Czech Republic: 116 123).
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. Six years later, their resting metabolism was about 700 kcal (calories) a day below where it started. Roughly 500 kcal of that could not be explained by their smaller body size or age. That is an extreme case, far from normal weight loss. With clients on a mild deficit it is gentler, but similar: the head wants to eat like before, and hunger lasts longer than you expect. In my experience, the harder the diet, the harder the way back to normal eating. 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 works best as a change you can live with for years. Set it up sensibly and your chances of keeping the weight off are much better. 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?
A smaller body burns less energy, and on top of that your body saves some energy on its own for a while. Losing muscle makes it worse, which is why protein and strength training matter. The effect of muscle alone is smaller than people think, but it adds up with everything else.
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 2.2 g per kg of body weight, or of your goal weight if you have a lot to lose) and strength training, which gives your body a reason to keep its muscle.
Why am I still hungry after a diet?
In Sumithran et al. (2011), 50 people with overweight or obesity did a 10-week very-low-calorie diet. A year later, in those who completed the study, several appetite hormones and hunger had still not returned to their pre-diet levels. Your body keeps the setting from the time you were losing weight. That doesn't switch off energy balance, but it makes it harder to hold, and willpower alone rarely beats it 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 I see working with clients is a gradual change in habits that you can keep for a year or longer.
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Apply for coaching Get the free Fat Loss KitSources, 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 coached 600+ clients through fat loss and the part after it. Evidence-based coaching for fat loss that lasts.
Apply for coachingThis article is for information only. It is not medical advice. If you have a health condition, talk to your doctor.