Have you been dieting for what seems like forever without seeing the results you’re hoping for? Maybe you’re even gaining weight and you’re frustrated, tired, and about ready to throw in the towel.

You may be asking yourself: Why am I gaining weight when I barely eat?

Could this be due to the way you have been dieting? Could the calorie restriction actually be backfiring and making you gain weight?

The short answer is: probably not. But we humans are complex creatures and a lot of factors can impact our weight and overall well-being. So let’s dive into how you achieve the weight loss you’re hoping for and what could be hindering your progress.

Can Eating Too Little Make You Gain Weight?

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What the science says

When it comes to weight loss, the science is clear that any approach that puts you in a calorie deficit will make you lose weight.

A calorie deficit means that you consume fewer calories from food and drink than your body uses to keep you alive and active.

This makes sense because it’s a fundamental law of thermodynamics:

  • If we add more energy than we expend, we gain weight.
  • If we add less energy than we expend, we lose weight.

But this is where the simplicity ends.

How many calories you’ll need to achieve a deficit is highly individual and will change over time as you age, your activity level changes, your metabolism changes, and your body fat percentage changes.

You can calculate your daily calorie needs using this formula, but this should only be seen as a starting point as the calculation can never take into consideration exactly how effective your metabolism is.

To find out why you aren’t losing weight, we need to look at some of the factors that can affect your metabolism

Can eating too few calories decrease your metabolism?

The body is a very intelligent machine in the sense that it knows how to effectively regulate its many processes to support homeostasis (keeping a constant weight).

In the context of dieting and weight loss, this means that if you restrict your food intake too drastically, your body will simply decrease its metabolic rate so it is burning fewer calories.

Of course, if your body begins to burn fewer calories each day, then it is going to be far more difficult for you to lose weight, but the problem is even greater than that.

If you aren’t providing your body with the energy it needs to fuel your daily activities, then it will have to begin sourcing it from somewhere else. You might be thinking the first place it will look is your stored body fat, but it will also begin breaking down your lean muscle mass so it can be converted to glucose and burned for energy.

This result is a snowball effect, where you are holding less muscle, meaning your metabolism begins to dwindle even further.

A study of contestants from the TV show The Biggest Loser was that if you have achieved dramatic weight loss very quickly, you may find that you now have to eat significantly lower calories than your peers to even maintain your weight.

If you decide to cut calories, never do it too quickly. When you first start dieting to lose weight, the best thing to do is to cut around 300-500 calories daily from your regular diet, or your ‘maintenance calories’.

Cutting just a few hundred calories each day will enable you to lose somewhere in the region of 1 – 3 lbs per week, which is just about right to make sure you are predominantly losing fat and not muscle.

If your weight loss stalls for a week or two, then you can simply cut another couple of hundred calories or consider adding a little extra exercise.

Tracking your calorie intake for weight loss

Unfortunately, most people who are trying to lose weight underestimate how many calories they eat daily. When we look at scientific studies, they find that 18 to 54% of people underreport how much they eat, and in some subgroups underreporting is as high as 70%.

This doesn’t mean that people are lying, but more likely that it is very hard to estimate food intake, especially if you didn’t cook the food yourself.

One way of assessing if you’re measuring your food accurately is to use a food scale to measure your food and keep an electronic food diary such as MyFitnessPal or CalorieKing. I recommend using a food scale rather than cups and spoons as it’s more accurate.

Another pitfall when it comes to estimating calorie intake is that some people will be very restrictive during the week and then “let go” and not track or pay attention during the weekends. I’m personally all for a relaxed approach to dieting but if you end up significantly overeating during the weekend, you might essentially end up no longer in a calorie deficit overall.

Other reasons you might not be losing weight while dieting

There are several reasons why people struggle to lose weight. Tackling the underlying issue can be what you need to reach your weight goals.

Some conditions and drugs can make you gain weight

Some conditions including Cushing’s disease, polycystic ovary syndrome, and hypothyroidism can make you gain weight or make it very difficult to lose weight.

If you’re experiencing unexplained weight gain or have struggled with these before it’s worth discussing the issue with your doctor and maybe have your medication adjusted.

Drugs such as steroids and some antidepressants may also cause weight gain. Don’t stop taking your medications but discuss doses or alternatives with your medical team.

You’re dieting, but not for weight loss

Dieting and eating less is in reality very subjective. Dieting for some means only eating whole foods, cutting out specific food groups, or no snacks or sweets, eating a meal less than they’re used to, intermittent fasting, calorie restrictions, and the list goes on.

But the thing is that you can be doing any of those things and still not lose weight if you’re not in a calorie deficit.

Reducing your calories has also been shown to lead to people being less active. Remember, a calorie balance is a balance of how many calories your body needs and how many you consume, so a significant reduction in your activity could tip the scale and halt your weight loss.

It simply takes time

Another common reason why people report not losing weight despite reducing their calories is that they don’t give it enough time. Our bodies will do their utmost to hold on to our fat reserves and you often have to be in a calorie deficit for a while before you will see any meaningful weight loss.

You might see an initial large drop in your weight the first week, but that’s most likely water and waste and you can’t expect to see that type of weight drop week over week.

Lack of sleep

Aside from time, another factor that could be impacting you is your sleep patterns. Sleep deprivation is often tied to higher BMI, although the exact correlation is unclear.  

Why undereating could be hurting your health!

If you do decide to continue eating very few calories, you should know that there’s a chance that you’re putting your health at risk.

When your body goes into starvation mode, you are at increased risk of both physical and mental complications, including

  • Abnormally low blood pressure and slow heart rate
  • Heart rhythm abnormalities
  • Hair loss
  • Brittle fingernails
  • Loss of menstrual periods in women
  • Dizziness
  • Trouble concentrating
  • Anemia
  • Swelling in your joints
  • Brittle bones
  • Depression

Undereating can also often lead to an unhealthy relationship with food, obsessively thinking about food, and potentially eating disorders.

If you find that you’re still not losing weight despite being in what you perceive as a calorie deficit while measuring out everything you eat and drink, you should:

  • Check in with your medical team for your annual physical and mention your weight loss journey
  • Increase your activity to increase your calorie deficit
  • Get enough sleep and reduce your stress levels to the best of your ability