- The key to weight loss is maintaining a calorie deficit, but consuming too few calories can actually hinder progress or even lead to weight gain.
- Low energy availability affects various bodily functions, including the secretion of thyroid hormones, which play a crucial role in regulating metabolism.
Why is a calorie deficit sometimes not enough?
When it comes to weight loss, you've likely heard about the importance of a calorie deficit — and if not, you can learn more in the article How to Calculate and Set Your Calorie Deficit? At first glance, losing weight might seem simple — just stick to a calorie deficit. However, while this is the theoretical foundation of weight loss, the reality is often more complex...The recommended calorie deficit should be around 15–20%. If the difference is smaller, it might not work effectively, as calculations of energy intake and output are often based on estimates only, and the reality might be slightly different. However, a deficit that is too large can lead to serious issues, which brings us to the main concern of this article. Too large a caloric deficit could lead to unsustainable weight loss, the yo‑yo effect or loss of muscle mass.
If, on the other hand, the dietary intake is so low that the body does not even meet its own physiological needs, weight loss will stop. In response, the body may start storing energy as fat to prepare for “worse times,” paradoxically leading to weight gain—especially in fat mass. In addition, weight loss is influenced by more than just caloric intake. Factors such as sleep quality, hydration, and stress levels also play a significant role in weight management.
Mechanism of stagnation or weight gain when dietary intake is too low
You've probably heard of "slowed metabolism". While this phrase is often used in marketing for weight loss products, the reality is that metabolism doesn’t slow down randomly. Instead, it is typically the result of an underlying condition, hormonal imbalance, or prolonged adherence to a very low‑energy diet.
If you eat too little, your body will start to conserve energy, gradually limiting functions that are not central to survival. Typically, this situation leads to changes in the concentration of certain hormones, and the reproductive system is usually the first to be affected. The thyroid gland plays a pivotal role in metabolic turnover. The results of studies show that female athletes with low energy availability and impaired reproductive system function had, compared to athletes without menstrual disorders and non‑sporting women, reduced levels of thyroid hormones. This points to the fact that too low an energy intake interferes with the normal function of the hypothalamic‑pituitary‑thyroid axis, and it can cause a decrease in metabolic turnover ("metabolic slowdown").
In addition, about 10% of the total daily energy expenditure is spent on the processing of food itself. So, if you reduce your intake to the minimum, you lose another part of your total energy turnover. And how much diet is too little? There's no single answer to this — for people with really no physical activity and a sedentary lifestyle, that threshold is likely to be around the resting metabolic rate (RMR) — the energy the body needs to cover all its functions at rest. For athletes, however, this RMR may be far higher than that and still be risky because they expend so much more energy through training that they end up with no energy left to cover basic functions. So, the more you play sports, the more you should make sure that you are effectively recovering the energy lost in training.
Weight loss plateau
Everything has been going well with your weight loss so far when suddenly, your progress stalls without any changes to your routine. This could be a weight loss plateau. When weight is reduced over a long period of time, the body's energy requirements decrease in parallel, as it simply does not need to supply as much "living matter". Moreover, if you have been following the same eating plan and workout routine for several months, your body may have adapted to the regimen, making it less of a challenge and slowing further weight loss.
The cause of this plateau is not fully understood, but it is believed to be a combination of these factors. Another possible explanation is dietary laxity — after months of controlled eating, you may have started snacking more frequently or incorporating more untracked meals. Occasional indulgences are perfectly normal and even beneficial in moderation. However, if they become too frequent, they can shift your calorie deficit into maintenance or even a surplus, halting weight loss.
What can you do to avoid stagnation and too‑low energy intake when losing weight?
1. Incorporate more exercise
You've probably heard that physical activity is one way you can quite dramatically affect your energy expenditure and, therefore, your weight loss effectiveness. In fact, it's not just about how big the calorie deficit will be but also the overall energy turnover. In other words, by exercising, you can consume more food and keep your metabolism "on track" due to higher energy expenditure. In addition, studies show that people with low energy expenditure and low energy intake are more likely to experience an increase in adipose tissue in the future.
2. Don't be afraid of strength training
Aerobic exercise is great for weight loss in that you burn a large amount of calories in a short period of time. However, strength training is also important as it promotes the growth of muscle mass, which is metabolically active. Thus, in this way, it helps to keep your metabolism going. In addition, after training with heavier weights, you can expect what is called EPOC, which means that your metabolism can work 6‑15% faster up to 24 hours after the workout.
3. Schedule "refeed days" from time to time
Refeed days and cheat days are not the same thing. While refeed means increasing your energy intake to (or at most slightly above) your balanced energy balance, cheat days are usually known as "ad libitum" intake, i.e., at will. However, both variants have a common goal: to prevent loss of motivation during weight loss, to "treat" yourself to something above the usual regime and also to prevent the aforementioned "slowing down" of the metabolism.
You can incorporate any of these strategies, but refeed days will help you keep your intake more under control, as it is also a controlled intake, just above your normal diet regime. For this reason, a refeed should last at least 2 days in a row. A cheat day, by contrast, is much looser, but with the risk that you will unknowingly eat so much energy that frequent inclusion will derail your weight loss efforts.
4. Check your diet settings
Before you incorporate any of the strategies mentioned above, make sure you have your diet set up correctly in relation to your goal. In particular, the emphasis should be on adequate amounts of energy, protein, fibre and fruits and vegetables. Try to focus on whole foods and foods with high nutritional value. The distribution of macronutrients depends on your preferences, but during weight loss, you should eat at least 1.4‑2g protein/kg body weight, 20‑35% of your total energy intake from fat and supplement the rest with good quality, especially complex carbohydrates.
5. Do you need to make sure you get enough sleep?
Low energy availability and sleep deprivation can lead to changes in the concentration of certain hormones. In this case, ghrelin, the hunger hormone, and the stress hormone cortisol will be on the rise. In short, nothing that you want when losing weight.
Bottom line
Calorie deficit is the essence of weight loss. But it's not the only thing that matters. In the long run, you should avoid an energy intake that is too low, which can negatively affect the functioning of your metabolism. It may even happen that if you eat too little, you will paradoxically gain weight.
To prevent this condition, it is advisable to include physical activity in addition to a properly adjusted diet. You do not have to worry about strength training. You can also try incorporating refeed days to help prevent your metabolism from adapting to low food intake.
