Carbohydrates and Weight Loss: Dispelling the Myths

Myth #1: Carbs make you fat

Truth: It's not the carbs—it's the sugar, bad fats, and calories

The truth is that every food can make you fat when consumed in excess. But when it comes to carbohydrates, it's also about the type of carb you're eating.

The theory that carbs make you fat is based on the carbohydrate-insulin hypothesis: diets high in carbohydrates are assumed to be particularly fattening because of their propensity to enhance insulin secretion.

This directs fat towards storage in adipose tissue and away from oxidation by metabolically active tissues, leading to an adaptive decrease in metabolic rate and thus weight gain and fat gain ^{1, 2}.

Here's how it works.

When you ingest carbohydrates, the gut breaks them down into polysaccharides and disaccharides before traveling to the small intestine for absorption as monosaccharides.

After absorption, the subsequent rise in blood glucose stimulates insulin release from the pancreas, enabling cells to take up glucose and use it for energy.

But the tricky thing is that insulin also has the job of signaling the liver to store excess glucose as glycogen.

But as the liver can only store about 80-100 grams of glycogen at one time, anything extra—if muscle glycogen stores are full—gets converted to fat for long-term storage.

The last part of this process is where people lose their cool and where the myth that carbs make you fat comes from.

But keep in mind that fat storage is a normal body function; fat is constantly being stored and broken down to support various body functions.

What you have to remember, however, is that glucose is one of the major fuels for every organ in your body, perhaps most importantly, your brain.

Glucose serves as the brain's preferential energy substrate, and when glucose intake halts, there are mechanisms in place that enable the breakdown of glycogen to supply glucose.

Since insulin up-regulates fat storage and down-regulates fat metabolism, it seems logical to assume that keeping insulin levels low, as in with a low-carb diet, would limit fat storage and maximize fat breakdown.

Lucky for us, this theory has been tested time and time again. Researchers of a 2017 review were very clear that when you control calorie and protein intake, there's no energy expenditure or weight loss benefit from eating a low-carb diet over a high-carb diet ³.

At the end of the day, controlling your calories and portion sizes will be more effective than kyboshing carbs completely.

Myth #2: Low-carb diets are most effective for weight loss

Truth: Initially, they can be, but not for sustained weight loss

The number one reason people get excited about low-carb diets is the initial drop in weight that happens when you cut back on carbs.

More often than not, this weight loss is attributed to glycogen depletion, and the water attached to it, not actual fat loss.

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Some studies suggest that a low-carb diet's beneficial effects on weight loss may also be in part due to the individual's glucose metabolism.

One study compared three different diets in a Chinese population of overweight individuals.

They used a LF (low fat)-HC (high carb) diet (20% fat, 66% carbohydrates), a MF-MC diet (30% fat, 56% carbohydrates), and a HF-LC diet (40% fat, 46% carbohydrates) ⁴.

Researchers found that reductions in body weight were significantly greater in the LF-HC groups throughout the study period.

After six months, weight loss was 0.5 kg more than in the MF-MC, and 0.7 kg greater than in the HF-LC group, suggesting that decreasing carb intake doesn't always equate to weight loss.

Other studies suggest that higher protein intake may be more effective than low-carb at inducing weight loss and fat loss, which may be attributed to the efficacy of elevated protein energy-restricted diets to elevated protein-induced satiety and preservation of fat-free mass ⁵.

However, while evidence suggests that low-carb diets are effective for weight loss, research shows that after one year of following a low-carb diet, weight loss plateaus and does not differ from those who eat a low-fat (moderate carb) diet ⁶.

Basically, it boils down to the good old principle of everything in moderation. If sustained weight loss is what you want, don't go overboard on the carbs, but don't cut them out completely.

Myth #3: Our bodies don't need carbs

Truth: Glucose is the substrate that fuels every cell in the body

Yes, the body can indeed function without carbs. Still, with that being said, that's primarily if you're in a state of metabolic ketosis whereby the brain is obtaining fuel from ketones and other organs from glucose produced via gluconeogenesis (production of glucose from non-carbohydrate substrates).

Now, gluconeogenesis is a workable solution during periods of low carb intake, but it's a bit of a lengthier process to obtain glucose quickly. No source is broken down as efficiently and rapidly as carbohydrates to supply energy demand.

However, for most of the population that cuts carbs, they're not in ketosis, and their bodies are still relying on glucose for fuel, so when there's limited supply being ingested, fatigue sets in and you feel like crap, to put it bluntly.

Research shows that neurons have the highest energy demand in the adult brain and require continuous delivery of glucose from blood ⁷.

While the brain accounts for just 2% of body weight, it consumes over 20% of glucose-derived energy.

And what's more, glucose is also required to provide precursors for neurotransmitter synthesis and the ATP that fuels their actions ⁸.

However, what's interesting is that research shows numerous central nervous system pathologies are the consequence, and sometimes also the cause of disrupted central or peripheral glucose energy metabolism ⁸.

So, next time you think about cutting out carbs, you might want to think again.

Myth #4: All carbs are the same

Truth: Carbs are not created equal—there are simple and complex carbohydrates

If a carb is a carb, we'd all be binging on donuts and potato chips, thinking it's the same as eating an apple—but it's not.

All carbs are not equal, and some offer a more beneficial nutrient profile than others, which can affect your weight loss efforts.

One of the main problems with this myth is that when people think of carbs, they think about fries, pastries, bagels, white bread, and all the other simple carbohydrates that are immediately converted to sugar and contribute minimally in the way of nutrition.

In reality, there are three components to carbohydrates: fiber, sugar, and starch. But where we get confused is that we look at foods that contain all three and do not know what they are; in this sense, they're classified as either simple or complex.

Simple carbohydrates are found in foods that are predominantly composed of starch and sugar.

That includes white bread, white rice, pasta, pastries, and other sweets and healthy foods like fruit, vegetables, and dairy, which all offer substantial vitamins, minerals, along with fiber, and are part of a healthy diet.

Simple carbohydrates are digested quite rapidly in the GI tract and cause an immediate spike in glucose and insulin.

Complex carbs, on the other hand, are composed of starch, sugar, fiber, and vitamins and minerals, besides small amounts of protein and fat that help to slow down their digestion and cause a more sustained increase in blood sugar and insulin, thus providing a steadier supply of energy.

As you can see, some foods offer a better source of carbs than others. The trick here is to look for carbs that provide a more beneficial nutrient profile—vitamins, minerals, and substantial amounts of fiber to help slow the absorption process and prevent blood sugar and insulin spikes that signal fat storage.