Ask the Dietitian: Why under eating won’t help you lose weight

by Raia van Reenen

Eating healthy while in a calorie deficit is a sure way to lose weight but what happens if the deficit is too great?

Every day your body depends on food and energy to perform. The food you eat is broken down to provide energy to the body in the form of calories. Think of calories as the fuel your body needs. Not enough fuel for the day? Well, the day is going to be a slow one. The main types of food can be categorized as Carbohydrates, Protein, and Fat. Each food group is needed as part of a healthy, balanced diet:


> Carbohydrates

The main source of energy in our diet. Broken down into glucose, carbs are an important energy source for our brain and muscles.


> Protein 

Essential for the growth and maintenance of cells and tissues. Protein is broken down into amino acids, the building blocks, and used to repair and build new proteins or structures for various functions.


> Fat 

Important energy-dense nutrient to perform physiological functions such as regulating hormones and protecting your organs. Fat intake is also vital for the absorption of certain vitamins and minerals.


Unfortunately, adding restrictions to your diet to break down any stored fat for weight loss weight can't replace the intake of a healthy diet that includes all food groups. So, if you stop eating or don’t eat enough, certain functions performed by the body might are affected, of which the side effects can be serious.

So, how do you make a safe reduction in calories to lose weight without causing any harm? First, let’s talk a little bit about the physiology behind it. Our bodies are adapted for survival and stability which is regulated through energy. Under usual circumstances, your body will acquire energy from your food, use as much of it as possible for all of its various functions and then store the excess as fat. However, if you reduce your dietary intake too quickly and/or by too much by undereating, it will cause a shock to the system. This shock will cause your body to become more conservative in how much energy it uses. Usually, this means slowing things down and retaining what energy stores it has, i.e., fat stores, and getting rid of ‘expensive’ metabolically active tissues that use a lot of energy i.e., muscles.

The side effects of undereating include feeling sluggish, weakened immune system, anemia, muscle loss, hair loss, poor sleep and even changes to the menstrual cycle. Long-term, undereating can lead to a syndrome of undernutrition.

But we can work TOGETHER with our bodies. When we gradually enter a calorie deficit, our body can learn to adapt along the way, almost realizing: “Hey, I can survive on this!”. By implementing a deficit gradually, bodily processes can continue as normal and fat stores can be utilized and reduced as needed without detriment to your muscles.

Another method of losing weight is to increase your muscle mass. Remember, muscles are metabolically active and use energy simply by existing. So, the more muscle you have the more calories you burn. However, developing, maintaining and repairing these energy ‘expensive’ tissues requires a minimum intake of calories.  One sucker punch of our physiology is that the process of breaking down muscle is much easier than breaking down stored fat which means that an underfed body is going to look for energy from muscles first. This is often why we start to see undesirable changes in our body composition when we start dieting to lose weight: weight loss due to reductions in muscle mass and not stored fat.

So how much food is enough?

Dietitians with a focus on sports nutrition like myself will do assessments and use calculations based on your fat-free mass i.e. your metabolically active tissue to determine your needs. I am able to do this by using my InBody scale to do a full body composition scan which is included in our first consult.  From here, I can work out your energy requirements and break them down into carb, protein and fat. I can use this to create meal plans based on your goals whether it’s fat loss or muscle gain.

Certain body compositions are beneficial for performance in different sports. Endurance runners, cyclists, bodybuilders, or those just wanting to be healthier all have different needs, so how could the method for each be the same? Long-distance athletes need adequate muscle and fat for power and endurance whereas weight-lifters prefer a lower fat muscle to muscle ratio for quick explosive strength movements.

Remember, that any effort to become healthier and/or lose weight, it should be safe, sustainable and make you happy! Overall health and happiness should never be compromised.  


Raia van Reenen is a registered dietician at Thrive. Raia has completed training through the Centre of Diabetes and Endocrinolgy for Diabetes management and is an Optifast Registered Dietitian,  Allergy training through the Allergy Foundation of SA, is a practitioner for DNA Testing and  Nutrigenomics  through 3x4 Genetics as well as completed a  course in Sports Nutrition. 



June 02, 2021 — KoaKoa Active

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