Low-carb diets skyrocketed in popularity decades ago when the very low-carb Atkins diet came on the scene. This style of diet has morphed into other variations on the low carb theme and are still popular among people looking for ways to lose and maintain their weight.
By definition, a low-carb diet contains fewer carbs and more fat and protein than a standard diet. However, low carb eating plans involve varying degrees of carb restriction. The most extreme low-carb diets allow no more than 20 grams of carbohydrates per day during the induction phase and 50 grams or less during maintenance. Carb restriction of this magnitude sends people into nutritional ketosis, where ketones bodies in the bloodstream rise. The ketones serve as an alternative fuel source during periods of starvation and come from the breakdown of fat. The principal reason people go on a low-carb diet is to lose body fat, although they may help with blood sugar control too.
Few people talk about the downsides of being on a very low-carb diet. For example, when you first start such a diet, you may experience fatigue, headache, and even flu-like symptoms as your body adapts to burning fat as fuel. After two weeks, these symptoms often subside, but there are still some dietary components and nutrients that you can fall short of on a low-carb diet. Let’s look at some of these.
Low-carbohydrate diets are high in protein and fat, so low-carbers often fill their plates with meat and dairy to get full without adding many carbohydrates. When you add fruits and vegetables to your plate, it increases the carb count, and if you’re only eating 50 grams of carbs per day, you can quickly exceed your carb allotment.
Most low-carb diets recommend eating only leafy greens and other non-starchy vegetables in moderation. They don’t recommend fruit except for berries since they’re low in natural sugar. Whole grains are relatively high in carbs, although they’re nutrient dense and have minimal impact on blood glucose, unlike ultra-processed carb sources. Fiber slows the movement of food through the gut, so it helps with blood sugar control.
Another benefit of a fiber-rich diet is it helps foster a more diverse gut microbiome, the bacteria that call your gut home. These bacteria play a key role in nutrient absorption, digestion, and immune health. Some studies also show that a diet higher in fiber protects against cardiovascular disease. Research reveals that the average person gets only half the recommended quantity of fiber each day and following a low-carb diet makes it even harder.
Humans, guinea pigs, and primates are the only animals that can’t make their own vitamin C. Humans and these species lack the enzyme that converts glucose to vitamin C and must get it through diet. In fact, a severe deficiency of vitamin C can be fatal. At one time sea voyagers died because they didn’t have access to fruits and vegetables on their journeys. You need vitamin C for immune health and to fight oxidative damage by acting as an antioxidant. Without enough vitamin C, the health of your skin and joints suffer too.
The best source of vitamin C is fruits and vegetables, dietary components that low-carb diet followers don’t consume a lot of. Many people who follow a low-carb diet eat no fruit at all. When they eat vegetables, it’s usually leafy greens. Leafy greens are a good source of vitamin C, but cooking can destroy up to half of the vitamin C content of vegetables. So, it’s not hard to see how low-carbers can fall short of vitamin C.
You need magnesium to support over 300 chemical reactions that support mental and physical health. Magnesium is involved in maintaining healthy bones and a healthy heart. In fact, it plays a key role in relaxing blood vessels and normalizing blood pressure. Magnesium is abundant in many plants-based foods, including leafy, green vegetables, nuts, seeds, and whole grain foods. Most people who eat a low-carb diet don’t eat consume of these foods to optimize their magnesium status. Some sources even say that the flu-like symptoms low-carbers get when they first reduce their carb intake is related to low dietary magnesium.
You can get some magnesium from meat and fish, but plant-based foods are the best sources. Some sources say that up to half of the population has low tissue levels of magnesium. These may not be picked up by a routine blood test for magnesium since it doesn’t measure tissue levels.
Very low-carb diets are often low in two B-vitamins, thiamine and folate. Both vitamins play key roles in energy metabolism. Folate deficiency can lead to a type of anemia while you need thiamine for healthy function of your nervous system. You also need more folate during pregnancy to prevent neural tube defects in the fetus. Vegetables, especially green, leafy veggies, are among the best sources of folate. Packaged foods, like breakfast cereals, are often fortified with folate but these foods are often high in carbs, making them off-limit to people who follow a very-low carb eating plan.
How about thiamine? Good sources of thiamine include tofu, acorn squash, beans, flaxseed, green beans, cauliflower, kale, and whole grains. You can get thiamine from pork and seafood, although not everyone eats an abundance of these foods.
The Bottom Line
You don’t have to go on a low-carb diet to lose weight. The key is to avoid ultra-processed carbs, added sugar, and eat more mindfully. Studies show that you may lose more weight initially on a low-carb diet, but a year down the line, the weight loss is similar. It’s also not clear what the long-term effects of a very low-carb diet are. Instead, lower the risk of micronutrient deficiencies, make smarter carb choices. The carbs in a plate of broccoli has a different effect on your body than the carbs in a doughnut. Choose wisely and you won’t have to count carbs!
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