Why do we gain weight after dieting?

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What is a diet?

When you think of dieting, what do you think of? ‘Must eat less than 1200 calories’ or ‘must eat clean’ or ‘must eat low carb and low fat’ or even ‘must choose healthier options’ Right? Don’t worry we will go in depth of weight loss and weight gain!

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However, more or less this is the methodology. People restrict themselves of their favourite foods and snack to then later face the worst cravings at which point 90% of the time people give in and potentially eat more than they would have if they ate when they initially felt hungry.

Within one year of post diet, approximately 80% of people will gain the weight back on. Within 2 years, about 85% of people will gain the weight back on and within 3 years that number increases to 95% (Norton and Baker, 2019). So, why do we gain weight after dieting?

Why did I gain weight after I lost it?

During a dieting phase, your body will face certain changes, especially to changes to your hormones that are responsible for your appetite but also changes to your metabolism.

To put it in a better perspective, your regular metabolism will be burning calories at a specific rate (metabolic rate). Whereas, if you are looking to lose weight you will need to reduce your calories for a prolonged period of time which causes your metabolism to decrease.

Therefore, as your metabolic rate decreases to burning reduced amount of calories, your body fat will begin to overshoot.

So how does this work?

Your body is very clever; it has its own defence system, and this is called the ‘starvation mode’.

During a caloric restriction (diet), your body will naturally make hormonal changes and metabolic changes to defend itself from any further weight loss. You’ll know when this happens because that’s when you’d reach a plateau with your weight loss. If you monitor your body changes closely, you’ll realise when the changes have slowed down. All those biological changes causes your body fat to overshoot. This means your body fat is on stand by to catch any calories and nutrients it can. So, once you give your body enough food for energy, it will grab all it can to restore what you have depleted it from, and prevents the weight loss from happening again.

REMEMBER! Diets have less than 5% success rate and people who relapse to their previous weight, 1/3 to 2/3 of them will gain even more than their pre-diet weight (Norton and Baker, 2019).

The first stage of the defence system

The first stage of the defense system can be named as metabolic adaptation. This is to defend your body against the caloric restriction you have placed it under. Essentially, your metabolism slows down to defend against starvation.

The best way to describe this process is with an example. So, lets presume that before you began your diet you consumed 2000 calories per day. Then, you decide to go on a diet on which you’d eat 1500 calories per day. The defence system will be triggered at that point. How? Because when you are hungry, which you will be on a diet, your body begins to break down your body fat cells in order to release calories from them for your daily activities and exercise. When your body fat starts to break down, a hormone called leptin responds and sends a signal to your brain.

How does leptin hormone work?

Think of it as an air conditioning system, the temperature is set at a specific temperature so if it falls below that temperature it will turn on to raise that temperature back to that set point and vice versa, if the temperature goes higher than the set point it will turn off to bring the temperature down.

The hormone Leptin works in the same way. The body fat set point is sensed via the size of each individual fat cell, as these fat cells begin to shrink during ‘starvation mode’ they release less leptin which reduces your metabolic rate and it tries to drive it back up by increasing another hormone called ghrelin which skyrockets your hunger. A lot of people will give into that hunger and overeat so those fat cells expand again. This will increase the metabolic rate and there it is back to its original set point.

It’s not just short term dieting, even people who have been dieting for months or years, their body will fight back to its original set point.

The last step of the defence system

By now you should have a fair understanding on how a diet makes biological changes to your body. Therefore, you’ll know that due to those biological changes your body prepares itself for weight regain before you even finished your diet by increasing hunger and reducing your metabolism. What does this mean for you? It means your body will be much more efficient at storing body weight.

You’re about to learn the last step of the defence system, but the best way to do this is to continue with the initial example. Remember, before you began your diet you consumed 2000 calories per day, then you reduced your calories to 1500 to lose weight. Let’s now say you have completed your diet and you are happy with your weight loss and begin to eat 2000 calories again. By this point, all those biological changes have occurred and your metabolism have slowed too which means that you will now be over eating by 500 calories.

Normally your fat cells would shrink during a diet where you lose weight but post diet, your fat cells will expand, and sometimes, depending on how drastic was your weight loss, your body’s defense system can also create new fat cells. This is the reason why people post diet can gain more weight than pre-diet. Yes, you heard correctly.

Continuing with the example

So! When you reduced your calories by 500 calories your metabolic rate slowed to burning 1500 calories per day, meaning now, those 1500 calories became your maintenance calories.

Therefore, once you complete your diet and go back to consuming your initial 2000 calories per day you will now be over consuming by 500 calories per day. At this point, the body will come across enough fuel (food) to replenish its resources of fat and defend itself against any further depletion by creating extra fat cells. In other words, it will capture all the food and ‘extra’ calories it can and store it within the body in case you try to diet again.

How to maintain weight after losing it?

In order to maintain your weight loss and minimise weight regain you need to speed up your metabolism. The best way to speed up your metabolism is through High Intensity Interval Training (HIIT) and Reverse Dieting. You can find out more on reverse dieting here. If you have been struggling to lose weight and you feel like there could be more involved, you can now do a weight loss test that identifies reasons why you are losing or raining weight. Check out the test here.

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In conclusion, the best diet you can go on is one you can adhere to. Diet becomes a lifestyle, it’s not just a diet. If you are planning to do intermittent fasting or a ketogenic diet, just ask yourself if you can do this as a lifestyle? If you can, perfect go ahead. But the only thing that will drive your weight loss is a caloric deficit (eating fewer calories than your body’s requirements). And, the only thing that will reduce your weight regain is reverse dieting.

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Norton, L. and Baker, P. (2019). Fat loss forever. 1st ed

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