1. Your body stores carbohydrate, mostly in your liver and muscles, in the form of glycogen. Depending on your size, you can store roughly in the range of 1500-2000 calories of storage carbohydrate (although that number is fairly variable based on your fitness and size).
2. If you’re sedentary and don’t really exercise much (which I don’t encourage), this amount of storage carbohydrate is more than sufficient to get you through a typical day. Really, your body only needs a maximum of 600 calories of carbohydrate to survive each day – and that carbohydrate can be derived from diet, or from you own storage glycogen.
3. But if you’re active and at the same time consuming a low carbohydrate diet, you can easily burn through your liver and muscle glycogen stores in anywhere from 2 days to a couple weeks. The nice part about this, if you’re trying to lose weight, is that since glycogen carries up to four times it’s weight in water, a low carbohydrate diet can quickly shed 5-10 pounds (or more), which seems quite satisfactory. But the problem is, most of what you’ve lost is A) energy to sustain intense physical activity and B) water.
4. So now you have very little storage carbohydrate and are potentially dehydrated. If you’re an athlete or a physically active individual, this means that you’re limited to utilizing fat as a fuel for energy. Fat, through a process called “beta-oxidation”, can provide tens of thousands of calories of readily utilizable fuel, but the problem is that it burns far more slowly than carbohydrate.
5. This means that if you’re on a strict low carbohydrate diet, you can say goodbye to intense weight training, track intervals, or just about any activity that would be consider “tempo”, “threshold”, or “intervals”. And this is the stuff that adds lean muscle to your body, boosts your metabolism and gets you fit fast – compared to a slow and sluggish slog in your “fat-burning zone”. This is not negotiable by your body. It is simple physiology. When you deplete muscle glycogen, there is a directly proportional increase in muscle fatigue, and also an increase in muscle catabolism (direct metabolism of your body’s own muscle protein, or conversion of that protein into glucose via gluconeogenesis). Many people on a low-carbohydrate diet simply stop exercising, because it can suck so much.
6. As you lose muscle mass, your already handicapped metabolism drops even more. I will acknowledge that muscle fibers don’t burn as many calories or boost your metabolism as much as we all like to think, but this is still an important consideration for those trying to maintain lean muscle mass or tone.
7. For active people, this trouble may all be “in vain”. Since physically active individuals and athletes are far more sensitive to insulin and less susceptible to blood sugar fluctuations, any attempt to eat low carbohydrate in conjunction with exercise, for the pure purpose of “controlling blood sugar levels” could be a mostly unnecessary endeavor anyways.
8. Low carbohydrate diets, if implemented improperly, result in low fiber intake from a sharp reduction in plant-based food consumption, which can increase risk of digestive cancers and cardiovascular disease, and also leads to constipation and bowel issues. In addition, a drop in fruit, vegetables, legume and grain consumption can result in inadequate phytonutrient, antioxidant, vitamin C and potassium intake. Many (but not all) low carbohydrate diets have these problems.
9. Typical “low carbohydrate” meal replacement bars and shakes, ice creams or ice cream sandwiches, and other low carb or sugar-free snacks often contain potentially unhealthy ingredients like maltitol, and are chock full of preservatives and highly processed ingredients. If your low carbohydrate diet involves boxed, wrapped and packaged food, it probably falls into this category.
10. There can be long term health issues as your body is chronically carbohydrate depleted over extended periods of time. Your liver is exposed to extra stress as it is forced to assist with manufacturing glucose from fats and proteins, potentially toxic amounts of ammonia are produced as proteins are converted into glucose, your body has a more difficult time producing mucus and the immune system becomes impaired as risk of pathogenic infection increases, and your body loses the ability to produce compounds called glycoproteins, which are vital to cellular functions.
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