The Dark Side of Low-Calorie Diets: 6 Negative Impacts on Your Health

In today’s image-conscious society, the pursuit of a leaner physique often leads many people to adopt low-calorie diets in the hope of dropping kilos quickly. The majority of promotional activity around calories boils down to eat less; weigh less. It often neglects the nuances of nutrition that render that irrelevant.

While calorie restriction can lead to weight loss, it’s important to understand that not all calories are created equal. Drastically cutting your calorie intake can have serious negative consequences for your health.

In this blog post, we will delve into the dark side of low-calorie diets. We will discuss 6 negative impacts on your overall health and well-being. 

1. Slower Metabolism

A prolonged period of calorie restriction can slow down your metabolism, making it more challenging to lose weight in the long run. This is a process known as metabolic adaptation. This is when your body senses a decrease in calorie intake, it adapts by conserving energy, which means you burn fewer calories at rest. As a result, you may find that you need to eat even fewer calories to continue losing weight. This creates a vicious cycle of deprivation and metabolic slowdown.

This is why it’s important not to start with too great of a calorie deficit. Although it takes longer, the smaller the deficit, the more realistic your weight loss is. This also often makes it more sustainable in the long run. At Fresh Fitness Food, we recommend starting with a 10-20% deficit. We do this to make sure it’s not too low to begin with. This also gives you the best chance possible to achieve your results, by giving space for further calorie reductions should your progress stagnate.

2. Nutrient Deficiency

One of the most significant drawbacks of low-calorie diets is the potential for nutrient deficiency. When you severely restrict your calorie intake, you’re not only reducing your energy intake but also limiting the essential vitamins, minerals, and other nutrients your body needs to function optimally. 

While this reduction is minimised with a smaller calorie deficit, if extreme, dieting and eating a very low amount of calories, can, over time, lead to deficiencies. These deficiencies are usually in nutrients such as vitamins A, C, D, E, K, and various B vitamins. They can also be in essential minerals like calcium, magnesium, and potassium.

3. Muscle Loss

Low-calorie diets can also lead to muscle loss, which is detrimental to your metabolism and long-term weight management. When your body is not getting enough calories to meet its energy needs, and its fat supplies are reduced by weight loss already, it often turns to breaking down muscle tissue for energy.

This will decrease your muscle mass. It but can also reduce your basal metabolic rate, making it harder to maintain or lose weight in the future.

4. Hormonal Imbalances

Low-calorie diets can disrupt hormonal balance in your body. For example, a severe calorie deficit can lead to decreased levels of thyroid hormone. They play a crucial role in regulating metabolism. Additionally, it can impact sex hormones like oestrogen and testosterone, potentially affecting reproductive health and libido.

In women, low-calorie diets can lead to amenorrhea, which can have a long-term impact on fertility. Starvation causes a drop in oestrogen, without which you won’t ovulate or menstruate, which can cause infertility.

5. Mood and Mental Health

Calorie restriction can also have a significant impact on your mood and mental health. Low-calorie diets are often associated with increased irritability, mood swings, and feelings of anxiety and depression.
This is partly due to the physiological stress that inadequate calorie intake places on the body and brain. There are also other causes, such as a reduction in sleep quality, blood sugars being less balanced, and your hormones perhaps feeling a bit off in general.

6. Fatigue and Weakness

Similarly to the above, when you don’t consume enough calories, your body lacks the energy it needs to perform daily activities. Because of this, your body has to work overtime to get its usual tasks done – the ones you tend not to think about, such as breathing, muscle contraction, or blinking.
This can lead to constant fatigue, weakness, and a reduced ability to concentrate and focus. Over time, it may become challenging to maintain a normal daily routine, let alone engage in physical activities, particularly if you’re consuming fewer calories than your basal metabolic rate.


While low-calorie diets may promise quick weight loss, the negative impacts on your health are undeniable. Nutrient deficiencies, muscle loss, a sluggish metabolism, hormonal imbalances, mood disturbances, and physical weakness are all potential consequences of prolonged and severe calorie restriction. Not to mention, it will ultimately result in weight loss, rather than fat loss. This is because eventually, your body will need to resort to other energy sources, such as muscle (including organs, in extreme cases).

It’s important to approach weight loss and healthy eating with a balanced and sustainable mindset. Focus on nourishing your body with the right nutrients rather than simply counting calories. Consulting a healthcare professional, registered dietitian, or qualified nutritionist for guidance on a balanced and personalised approach to weight management is always recommended.


If you’re unsure of a suitable calorie target for yourself, feel free to book a call with one of our Nutritionists, or allow our order form to calculate this for you!

Georgia Chilton

Published by Georgia Chilton

In her teenage years, a love of food and rowing led Georgia into this field as she wanted to know how to optimise performance through nutrition. With a BSc in Nutrition and an MSc in Sports and Exercise Nutrition, she has the skill set to help you track towards your goals and maximise your potential.

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