Undereating – Why is it bad?

So you’re wanting to lose weight so you think “ok let’s cut out lots of Food, that should work” – Nope!!! Unless you keep your eating habits healthy you could hamper your chances of losing weight by under eating. Yes, we want a calorie deficit but too large a deficit has its dangers. Here’s why undereating is not a good way to lose weight!

So a couple of days where you don’t manage to get your minimum calories wont to anything much, but for lots of people it becomes a way of life, and as they don’t lose weight they become stricter and cut the calories even more.


picture of healthy food and fruit.Under-eating = BAD!!



Our bodies have enough stored energy to meet our needs for 1-3 months in the form of muscle and fat, however the body can only store 1-2 days’ worth of glycogen (carbohydrates) which if not topped up from our diet is very quickly used to keep our blood sugar levels even.

When our bodies haven’t been receiving enough calories for several days the body starts to enter “energy-conservation mode” or starvation mode, this means your metabolism slows down, and in turn you have less energy, so you feel tired and can start to feel fatigued (not great for working out).

When you don’t eat enough calories, your body will start to look at other sources, your fat and protein stores within the body and will start to break down protein sources (muscles) to use instead. Such diets such as the Keto diet use this principle to make the body use the fat stores, but they have to make sure that they have a high protein intake also to counter the effect on the muscles, (they also still have a small amount of Carbs, to maintain the minimum blood sugar levels).

Your body needs to keep a minimum blood glucose otherwise your body continues to break down muscles and organs. It’s a major problem in the long run, because your body doesn’t distinguish between essential tissues (think: heart, kidney, blood cells) and less essential tissues (think: skeletal muscle). Over time, this breakdown weakens and damages your vital organs.

There are many reasons why we need to make sure we are eating enough to properly fuel our bodies. For more information on low blood sugar levels check out


alongside these problems you also run the risk of malnutrition. When you don’t eat enough food then it’s likely that you won’t be getting the right Micro-nutrients (vitamins) which the body also needs. Which causes more problems.

Going back to my first post on calories, you BMR is the basic metabolic rate for your body, its not steadfast but it gives you a good guide to how much you should be aiming to eat. Then we multiplied it by our activity, so when we use more energy we need more, this helps the body maintain its health, especially whilst we are losing fat, we still need to ensure the body has enough calories and nutrients to maintain good health. If you are on a low calorie diet, please don’t just follow it like a sheep but question why!

I would always create a calorie deficit through exercise and not by cutting more and more calories. So that your body isn’t getting what it really needs.


Three main reasons not to under eat (there are more).

  1. Slows down your metabolism.
  2. Organ Functionality and muscle decrease.
  3. Risk of Malnutrition

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