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Can you gain weight in a caloric deficit?

We’re taking on a controversial, largely misunderstood topic here: can you gain weight whilst eating in a caloric deficit?

To assess this, let’s look at the energy balance principle : energy intake - energy expenditure = changes in body weight. If this equation is a positive energy balance, weight is gained. If this equation is a negative energy balance, weight is lost. Right?

In actuality, it’s not always the case. Generally speaking for an average, sedentary individual who maintains the same activity level but starts to eat less, they will lose weight, or eat more and gain weight. But it’s not possible to claim it as irrefutable, as there are exceptions. Here’s why.

Body weight changes are not always reflective of body fatness changes, so we have to be more specific. For example, if you eat a ketogenic diet at maintenance or even in a surplus, you are going to lose weight. This is because ketogenic diets cut out carbs. Each gram of carbohydrate is stored in the body bonded with three grams of water (to make glycogen), so when you cut the carbs, you’re going to lose a lot of water (body) weight.

This was shown in a 1976 study that compared weight loss in a group on a ketogenic diet vs. a group on a regular diet, both on the same number of total calories. The ketogenic group lost significantly more weight, but on inspection, actually lost less fat than the regular diet group, but just lost double the amount of water. Thus - weight changes do not necessarily correlate to caloric intake, and are not always reflective of fat loss.

To answer the aforementioned question of whether you can gain weight in a deficit, here’s why you can. If you’re on a high carb diet eating in caloric deficit, you might still gain weight. This is because, as mentioned, carbohydrates bind with water. Carbohydrates are also typically higher in fiber, which bulks out stools adding mass in your digestive tract, increasing your total body weight.

Furthermore, you can gain weight in a deficit if you’re gaining muscle and losing body fat. A study published in the International Journal of Sports Nutrition and Exercise Metabolism put a group of athletes on a caloric deficit while they continued their athletic training. The researchers found that despite the caloric deficit, the athletes gained body weight due to increases in their muscle mass.

These examples refer to water weight and lean body (muscle) mass, rather than fat. But hypothetically you can also gain body fat whilst in a deficit, if you are gaining muscle faster than body fat changes. This is because your muscle mass increases your body weight and the amount of calories you need to eat in a day to be at maintenance, thus shifting you into a deficit. However, this is unlikely for the average person unless you have freak muscle building genetics, or you’re on steroids.

Ultimately, you can gain body weight while in caloric deficit, or decrease weight in a surplus. It’s important to be specific about the differences between body ‘weight’ and body ‘fat’, and measure these separately throughout your fitness journey to ensure you’re not drawing the wrong conclusions of your progress.

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