The right carbs fuel your body and brain and supply an abundance of nutrients, too.

Low-carb diets are nothing new – in fact, they’ve been around for more than 100 years. Since that time, they’ve cycled in and out of popularity. Dieters are often drawn to them because they promise fairly rapid weight loss. And, with a focus on protein and fat, low-carb plans do a pretty good job at controlling hunger. But very low carb diets have some downsides, too.

Why are carbs important?

Carbs don’t really deserve their bad reputation. In fact, they’re your body’s primary fuel source. When you eat carbs, they are broken down into a sugar, called glucose, which is transported in the bloodstream to your cells, tissues and organs. While your entire body relies on a steady supply of glucose, your muscles actually store glucose – in a form called glycogen – to provide quick energy, and your brain depends almost exclusively on glucose for fuel.

Carbs are found in lots of foods – some are very healthy, and some aren’t so good for you. Vegetables, fruits, whole grains and beans are healthy, natural sources of carbohydrates. These foods provide not only the carbs your body needs, but an abundance of vitamins, minerals, fiber and phytonutrients (many of which act as antioxidants and protect the health of your cells). The problem is that many people eat too many of the less-healthy carbohydrates – like those found in sugars and sweets as well as refined and starchy grain foods like white rice, pasta, white bread and refined and sweetened breakfast cereals.

What happens when you eat a very low-carb diet?

When you don’t eat enough carbohydrates to supply glucose to your cells, your body is forced to break down body fat for energy. Rather than producing glucose, the end result of fat breakdown are compounds called ketones (and how “keto” diets get their name). Your body is programmed to make this switch when you are starving in order to keep your systems running. When you eat a well-balanced diet, few (if any) ketones are produced. But, on a very low-carbohydrate diet, your body is basically tricked into thinking there is no fuel coming in, so it goes into a state called ketosis.

Eating the right carbs matters

While your body can adjust to running on ketones, keep in mind that this isn’t a normal physiological state – it’s a defense mechanism that your body employs to keep your engines running.

A very low-carb plan is unbalanced and difficult to sustain – which means that any weight loss that occurs is likely to be regained. Most importantly, a very low carbohydrate plan eliminates not just the unhealthy carbs like sweets, but also limits the healthy fruits, vegetables, beans and whole grains, meaning you’ll miss out on an abundance of nutrients that these foods provide.