This advice is getting to be almost as common, and is just about as dangerous, as “eat less and exercise more” for fat loss.

“I’m trying to lose fat, why would I eat carbs?” It’s become an assumption that goes without saying. Bread, candy, juice, or even fruit, it makes no difference, “they all turn into sugar in your body.”  While that is partially true, you’ll understand by the end of this article why it may not be such a bad thing after all.

Why would reducing carbohydrate intake lead to fat loss? Where does this idea even come from?

The concept of reducing carb intake to lose fat and be healthy has been around for decades and has led many, including myself, down a treacherous path. Much like the “eat less and exercise more” recommendations, this idea has led to misguided health and fat loss approaches such as low-carb-high-fat diets, intermittent fasting, fasted exercise, and low-intensity endurance exercise, among others.

There are a couple reasons why reducing carb intake for fat loss has become so highly popularized.

1. It does increase the amount of fat we burn. Our bodies have two primary options for producing energy: burning carbs and burning fat. Generally, the more carbs we eat, the more carbs (and less fat) we burn. So, on the surface it makes sense: burn fat to lose fat, so eat fewer carbs to lose fat.
2. Weight loss does happen when you take out carbs, and pretty immediately too. But, this weight loss isn’t the healthy fat loss we’re looking for. Instead, it primarily occurs for 2 reasons: water weight and stress.

Low-Carb Diets and Water Weight

Immediate weight loss on a low-carb diet is pretty common, but this weight isn’t fat – it’s water! There are two mechanisms by which taking out carbohydrates causes us to lose water:

1. We store carbohydrates in the form of glycogen, which holds on to water when it’s stored (3-4 grams of water for every 1 gram of glycogen) (1). So, what happens when you stop eating carbohydrates? Your body uses up its glycogen, and the water goes with it.
2. Many carbohydrates are hard to digest, especially if the metabolism is low. This results in irritation and bloating in the gut, which causes the body to hold extra water. So, when you take out these hard-to-digest carbohydrates, gut irritation and bloating are reduced, and so is the amount of water the body holds.

These two mechanisms can result in weight loss of 5-10 lbs. or more. Of course, most of us assume that this weight is fat, so we think the diet is working. In the meantime, dysfunction begins to occur and it isn’t until later that the symptoms become too great to ignore.

Low-Carb Diets and Stress

Cravings for carbs often begin immediately on a low-carb diet, sometimes coupled with moodiness and fatigue. Over time, more severe symptoms begin – sleep issues, brain fog, low libido, hair loss, a weakened immune system, and the list goes on. Sound familiar?

These are all the same symptoms of energy imbalance that you learned about in part 1 of this series! But why would symptoms from reducing carb intake be the same as energy imbalance?

Because carbohydrates are required for a high energy supply.

Carbohydrates are our bodies’ preferred form of energy. They’re broken down into glucose (yes, a form of sugar) which is then oxidized (converted into energy) for your body to use. If carbs aren’t available, then your body will settle for burning fat, its emergency energy source.

(If you’re not scientifically inclined, feel free to skip this next part)

One of the most crucial differences between oxidizing (burning) carbohydrates and fats is that carbohydrate oxidation produces 50% more carbon dioxide (CO₂) than fat oxidation. Carbon dioxide production is vitally important for many reasons, one of which being that it increases the amount of oxygen that comes into the cell (due to the Bohr effect) (2, 3). This oxygen is needed for energy production! The increased carbon dioxide production resulting in increased oxygen entering the cell allows carbohydrates to support a higher metabolic rate than fats (4).

When fat is oxidized, producing less carbon dioxide and allowing less oxygen into the cell, it acts as a signal that the body can’t produce enough energy. So, the body tries to conserve energy by reducing its metabolic rate. There are a few other differences between carbohydrate and fat oxidation, such as the production of NADH versus FADH₂, that act in tandem with CO₂ to reduce the metabolic rate, but that’s a topic for another time (check out this article if you want to learn more about these differences).

In other words, we need carbohydrates to produce a lot of energy. When our bodies rely on fat for energy production instead, they can’t produce as much energy. This results in the same cascade of events as “eating less and exercising more”: our bodies adapt by reducing their energy usage and storing food instead of using it to produce energy.

If we continue restricting ourselves of the carbs we need to produce energy, physiological stress occurs resulting in the breakdown of our emergency energy stores (fat, muscle, and other tissues) while further decreasing our metabolism, or energy production (5, 6). Like fat loss from “eating less and exercising more,” this comes at the cost of reducing the energy our body has available to function optimally, causing all sorts of problems. It also leaves us more likely to gain fat if we add carbs back in.

Hold on a minute… if avoiding carbs is not ideal for fat loss or health, does that mean that we can eat carbs again without feeling like they’re going straight to our waists? Without feeling like we need to go run on the treadmill after? Without feeling… guilty?

Yes! Please! Have your carbs and eat them too! We need carbohydrates if we want our bodies to have more energy and lose fat in a healthy way.

As I mentioned in Part 1 of this series, healthy fat loss occurs by increasing our bodies energy supply and decreasing its energy demand, which reduces its need to store fat as an emergency energy source. So, since burning carbohydrates produces more energy than fats, eating enough carbohydrates is extremely important for healthy fat loss! (4)

But, there are a few caveats. Not all carbohydrates are created equal. There are major differences between carbohydrate-containing foods (grains, beans, fruits, etc.) that determine how they are digested, their effects on blood sugar, and how efficiently they are oxidized, all of which affect fat loss and health.

Plus, as I mentioned earlier, certain carbohydrate-containing foods may cause gut inflammation and bloating. And, carbohydrate oxidation can be inhibited by things like stress hormones, a lack of vitamins or minerals, and polyunsaturated fats.

These topics are beyond the scope of this article and are just below the surface of what you need to know if you want to lose fat while getting healthier. To learn more about how to improve energy balance for healthy fat loss, sign up below for a free 6-day email series on Fat loss, Health, and Energy Balance.

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