Can You Gain Fat On A Calorie Deficit?

The only way to reduce body fat and improve your overall body composition is by staying in a calorie deficit. However, some people may notice they gain fat, instead of losing it.

As a general rule, you cannot gain fat on a calorie deficit. A calorie deficit is an effect of not eating enough calories. Over time, the body metabolically adapts and uses internal sources of energy (stored body fat) instead of using calories from the food intake, which causes fat loss.

However, it is not uncommon to see people dieting and gaining weight.

Can you gain weight on a calorie deficit?

As a whole, you cannot gain weight on a calorie deficit. When you’re in a calorie deficit this means the body has to use stored body fat as fuel because there is not enough food. In the effect, as fewer calories are consumed than expended, we lose body weight.

In other words, if you’re gaining weight, that means you’re not in a calorie deficit. You’re in a calorie surplus.

If you’re eating less than your daily energy expenditure, you will lose weight.

So if you’re noticing that you’re gaining weight, but not losing, you should recalculate your calorie intake.

Here’s the thing.

How do you really know you’re in a calorie deficit? A calorie deficit is nothing else than eating less food. But eating less is subjective. So you need some type of method to calculate your food intake.

How to measure your calorie deficit?

There are 5 ways to measure your calorie deficit:

1. Counting calories from food

Counting calories from food is a well-established method to measure your calorie deficit. However, counting calories does not provide information about the calories you burn daily. Way to find out your actual calorie expenditure (calories burned) you need to know your BMR, TEF, and physical activity.

BMR stands for basal metabolic rate.

To really split hair and establish the accurate BMR you need to be after a 12-hour fast in a strict laboratory chamber. They hook you up with a metabolic cart and calculate how much oxygen you consume.

TEF stands for the thermogenic effect of food. This is the number of calories used for digestion, food breakdown, and nutrient transport (source).

Physical activity is everything that you do when you’re moving around. Walking, running, house cleaning, carrying groceries, etc.

2. Measuring food portions

Measuring food portions include counting calories and weighing the food. Basically, you should know the calories for every gram of food you eat. And be sure to surgically weigh all those foods daily.

3. Counting food points

Some weight loss systems and diets like weight watchers or the zone diet calculate food points instead of counting calories. So for every food item, there will be a chart with the number of points that it provides. Depending on your current weight and your weight goal, you will have several points to stick to.

4. Mindful eating

Mindful eating is nothing else than intuitive eating. It’s all about listening to the body cues and paying attention to when you’re hungry, and when you’re not. The idea is that you start eating your meals when you’re physically hungry, and you stop eating when you’re satisfied.

5. Intermittent fasting

Intermittent fasting is basically the cycling of the eating window and not eating (fasting). Depending on the approach you choose, some fasting protocols like one meal a day allow you to eat once a day. Other approaches like alternate-day fast allow for one-day fasting, followed by one day of feeding time.

Can you be in a calorie deficit and not lose weight?

In general, you can be in a calorie deficit and not lose weight.

Losing weight on a calorie deficit will depend on a few factors, like the number of calories you consume, the duration of your calorie deficit, and the accuracy of your calculations that tell you how many calories you consume.


Weight loss is a process. Just like learning a new language, or growing a beard. It doesn’t work like a phone where you just click and it works immediately.

There is this delayed effect. You cannot expect to see results on day two if you changed your diet on day one.

Why am I gaining fat in a calorie deficit?

On average, gaining fat in a calorie deficit is caused by overeating your calories. A calorie deficit means you eat below your daily energy expenditure. And if you gain weight it is likely due to miscalculations of your actual calorie intake, or mindless eating.

Fortunately, there are only a couple of reasons why you may be gaining fat, or not seeing the results.

There are 2 reasons why you don’t see weight loss results:

1. The number of calories you consume is too high

This means you may think you’re in a calorie deficit, but in reality, you can be just eating too much food. The easiest way to really be 100% sure is to start a food journal. In the journal, you can write down the food you eat, and when you include every detail, you will see in black and white how much really you eat.

2. The duration of your calorie deficit is too short

You may be in a calorie deficit already, but you don’t see results, yet. Don’t worry. To really see the change it will take several weeks, sometimes even months.

So lower your expectations and instead of focusing on the outcome (weight loss) focus better on the behaviors (things that will lead to that outcome).

Is It Possible To Be In Too Much Of A Calorie Deficit?

It is possible to be in too much of a calorie deficit. Initially, the weight will go down. But eating an extremely low amount of calories for too long can slow down the basal metabolic rate, lower energy, and significantly increase the cravings for food that can cause overeating.

There are plenty of health benefits for doing calorie restriction. From cardio to immunity, to even longevity. But it all comes with the right dose. Just like exercise.

  • A 30-minute walk or gym workout can feel invigorating and energizing.

The same with calorie restriction.

The longer you stay in a calorie deficit, the more you will have:

  • Cravings
  • Stress
  • Emotional eating
  • Problems with sleeping
  • Fatigue
  • Mood swings

What happens if you stay in a calorie deficit for too long?

As a general rule, staying too long in a calorie deficit will decrease body weight and slowly reduce the resting metabolic rate. With less body weight, oxygen demands will decrease. This means the need for calories will drop and cause weight to plateau.

So in the beginning, the body is adapting to eating less food, and it uses body fat as a meal replacement. And the longer you stay below calories, you will eventually start losing weight (source).


With a lower body weight, you will burn fewer calories on a daily basis. This is the weight loss plateau.

How to avoid weight loss Plateau?

As a whole, a weight loss plateau happens after you’ve been dieting for a while and lost already a significant amount of weight.

With lower body weight, the body will adapt by lowering the resting metabolic rate and reducing daily calories burned.

There are 2 best ways to avoid a weight loss plateau.

1. Calorie cycling

Calorie cycling is a well-established method used to skip the weight loss plateau by introducing high-calorie days alternating with low-calorie days.

This tricks the metabolism by increasing the thermic effect of food, resting metabolic rate, and improving energy (source).

2. Carb cycling

Similar to calorie cycling, carb cycling is a well-known strategy to decrease body fat percentage and stay in a calorie deficit for an extended period of time.

Instead of focusing on general calories, during carb cycling, you divide days between the high carb (usually on training days) and low carb (source).

Can too much of A calorie deficit cause weight gain?

Too much of a calorie deficit can cause weight gain. In the short term, calorie deficit will reduce body weight. But in the long term, excess calorie deficit increases stress levels and food cravings, which can lead to unwanted eating behaviors like overeating or binge eating.

This happens more on the psychological level. With longer calorie restrictions, we are more likely to crack under pressure and choose to overeat.

The longer you diet, the more food you crave.

That’s the number one reason why people do the jo-jo diet. First, they set up some unreasonable goals. And after being strict like a soviet teacher they develop enormous cravings for food that adds so much stress that one day they crack under pressure.

Gaining fat on a calorie deficit is a clear sign that you’re overeating. The best solution will be to smoke out the actual problem and try to find an alternative way to measure your calories. So you can be 100% sure.

Michal Sieroslawski

Michal is an exercise physiologist (MSc) and a veteran endurance athlete. He loves to experiment and share his successes and failures to help busy men and women who want to lose weight.

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