Did you know the body’s main source of fuel is carbohydrates? General recommendations are that we consume about 50% of our calories from carbohydrates, but what happens when there’s a shift and why do some people follow low carb diets? If we need carbs but don’t eat them, then what fuel do we use? Carbohydrates are stored as glycogen in our liver and muscles. If we don’t use them, they are converted into triglycerides, one of the main components of our body fat. When we exercise, the body gets energy from the carbohydrates and fat we get in our food, but if we don’t eat, things are a little different. Untrained athletes can store 80 mmol/kg of glycogen in skeletal muscle. An endurance trained athlete can store 125 mmol/kg, and after following a high carbohydrate diet for a few days, up to 200 mmol/kg can be stored. So, the more physically fit we are, the more carbohydrates we can store, meaning we can participate in activity for a longer duration. Additionally, the liver can store up to 100 g of glycogen as well so getting the recommended amount of carbohydrates on a daily basis ensures your body will have adequate amounts of energy when it needs it.
When we eat food that contains sugar (carbohydrates), it enters into the blood stream and insulin, an anabolic hormone, is released. Insulin helps transport the glucose from our foods into the muscle or liver cells and that’s how we get energy from it to perform our daily activities and exercise. The brain uses about 15-20 grams of glucose within two hours of eating and about 100-145 g over the course of the day. As long as we consume glucose, the body will use it for fuel, and if we eat more than we use, we can save it for later, in the form of fat. This is one reason why carbs get a bad rap- if we eat too many, we gain weight, but in all honestly, if we eat too much of anything, we can gain weight. Additionally, when there are carbs in the system and glucose in the blood, there’s less breakdown of amino acids and fat as a source of fuel. This is why you read recommendations to have some carbs pre and post workout- they help spare lean body mass, your muscles, from being broken down to provide a source of fuel when we exercise (or participate in any other form of activity that requires energy).
So, what about low carb diets then? The goal of a low carb diet is to initially deplete the body’s stores of glycogen, deprive it of carbohydrates, and “train it,” or allow it to adapt to using fat as a source of fuel. In a starvation situation (not recommended), fewer carbohydrates are available and fats will be used. The liver cannot supply glucose so blood sugars drop, insulin levels decrease, fat breakdown INCREASES, and amino acids (the building blocks of protein that make up our muscles) are released from the muscle tissue. This means we can and will use both existing body fat and muscle mass to supply energy to the body, but again, that’s in a state of starvation, when we are not supplying anything to the body. If we keep that up, many changes take place on cellular, hormonal, and physiological levels, and eventually, we die. It takes about 60 days to die of starvation, which is obviously why NOT feeding yourself is not recommended, as mentioned above! Supplying the body with adequate amounts of fat and protein, however, while following a low carbohydrate diet, can minimize amino acid release from the muscles and maximize use of preexisting body fat as a source of fuel which is why many people find it to be a favorable diet for weight (body fat) loss.
Without carbohydrates, how does the brain get fuel? Ketone bodies, the production of which takes about 2-3 days, but become the brain’s primary source of fuel by week 3 of a low carb diet. They are a substance made from beta-hydroxybutryic acid and acetoacetic acid and via a long chain of complex events, they can be produced during starvation, when insulin levels are low, or if we eat a low carbohydrate, high fat (LCHF) diet. They are important because they are a substance that can provide fuel for the brain whereas fats cannot. Within 3 days, ketones will provide 30-40 percent of the energy needed but in that adaptation phase, the body will feel sluggish due to the drop in carbohydrates. It takes time, but once your brain and body adapts, you will feel better, no more “hangriness!”
There are many changes that take place when following a low carb diet. Glycogen is depleted, hormones shift, and there is an increase in fat breakdown to supply the body and brain with energy. Ketone production spares the body’s stores of protein and is a positive adaption so as to save protein to be used for necessary functions. Many people enjoy following a LCHF diet for its results with overall body weight loss. As long as it is a well formulated diet, there are many benefits of such a diet. Additionally, according to “The Art and Science of Low Carbohydrate Performance,” by Jeff Volek and Stephen Phinney, there are many implications for a LCHF diet in endurance activity, but for peak performance and high intensity activity, carbs are king. As always, choose an eating pattern that meets your needs and ensure it is well formulated and nutrient dense.