Why Do Carbohydrates Make You Gain Weight?

Too many of the wrong types of carbs can make you gain weight. (Image: PaoloBis/Moment/GettyImages)

Exercise and portion control are both excellent strategies in managing your weight, but they're only part of the story. Did you know that you can follow two different meal plans, with the same daily calories, and one can lead to weight loss, while the other leaves you at a plateau or even gaining weight?

The amount of carbohydrates in a meal is the key to losing weight and keeping it off because, unfortunately, the wrong types and too many carbs make you gain weight.


Eating too many (and the wrong types of) carbohydrates can make you gain weight by disrupting your glucose and insulin levels and promoting fat storage. Certain types of carbohydrates can also throw your gut bacteria out of balance, another factor that can contribute to weight gain.

Do Carbs Promote Weight Loss?

In the past, doctors often recommended a low-fat, low-calorie and relatively high-carb diet for weight loss. On this diet plan, your day might look something like this: a bowl of oatmeal and a banana for breakfast, a lean-meat, no-mayo sandwich on whole-wheat bread and grapes for lunch, and 3 ounces of lean meat, like fish or ground turkey, with potatoes (but no butter or sour cream) and plain steamed veggies for dinner.

You could lose weight on a diet like this, but there's a high probability that you'd have trouble sticking to it for the long run. It's likely that you'd be hungry all the time, not only because it's low in calories, but because your body would digest all of those carbs very quickly.

Without much fat or fiber to slow their absorption, the carbs would cause spikes and crashes in your blood sugar, which can also make you feel hungry. And when you feel hungry, you also feel deprived and are more likely to binge-eat.

Do Carbs Make You Fat?

So do carbs make you gain weight? It's true that eating too many carbs can make you gain weight, especially if they're low-fiber, high-glycemic carbs. Glycemic load describes the way your blood sugar levels are affected by the carbohydrates you eat.

High-glycemic carbohydrates move through the digestive system quickly and spike blood sugar and insulin. Low-glycemic carbohydrates are digested slowly, which prevents blood sugar spikes (and resulting crashes).

Over the years, the standard American diet has transitioned to highly processed foods with a high glycemic load, and this has gone hand-in-hand with an epidemic of obesity. High-carb eating triggers your body to store fat rather than burn it, which makes you feel hungry and less energetic.

How Carbs Lead to Obesity

Carbs make you gain weight for a variety of reasons. In the simplest explanation, many foods that are high in carbs are also high in calories, especially sugary sodas, pizza, muffins, cakes, ice cream and other desserts. Eating these foods regularly not only pushes you over your carb needs, but it provides too many empty calories as well.

Also, unless they're high in fiber, carbs are digested quickly, which means you're hungry again soon after eating them. Carbohydrates (especially refined carbs like sugar, rice, pasta or white bread) cause blood sugar fluctuations, which bring on a feeling of hunger and food cravings.

But, there's more: When your blood sugar is spiking, your pancreas produces insulin to maintain optimal blood sugar levels. The more insulin in your blood, the more your body converts carbs to fat that then gets stored in your body. Oftentimes, this fat is stored in your belly. If you continue to eat a lot of carbohydrates, the resulting high insulin levels reduce your body's ability to burn that stored fat.

Carbs and Weight Loss

Researchers at Johns Hopkins conducted a six-month study, comparing weight loss on a low-carbohydrate versus a low-fat diet. Although both groups lost weight, the low-carb group lost 10 pounds more, on average.

Additionally, the low-carb group lost more fat and less muscle, while the low-fat group lost more muscle and less fat. The more muscle you have in your body, the more your body burns fat and calories. Based on this evidence, researchers concluded that a low-carb diet is more beneficial to weight loss than its low-fat counterpart.

Carbs and Insulin Resistance

If you follow a high-carb, high-glycemic diet for a number of years, it's likely that you'll end up with a condition called insulin resistance. If you have insulin resistance, your cells are not able to effectively use insulin and your blood sugar levels rise, usually leading to pre-diabetes and, if left uncontrolled, Type 2 diabetes.

Even though your body isn't able to effectively use the insulin, your pancreas is still producing it, leading to a greater storage of fat, a large percentage of which is stored in your belly. This fat, which is stored around your liver, pancreas and intestines, is called visceral fat, and it can be especially problematic.

The Dangers of Visceral Fat

Visceral fat is an "active fat," which means it affects the hormone function in your body. Having a lot of visceral fat increases your risk of developing serious health problems, including:

  • Diabetes
  • Heart disease
  • High blood pressure
  • Stroke
  • Certain cancers

A study published in the Journal of Nutrition in 2015 reported that participants who followed a low-carbohydrate diet lost more visceral fat than participants eating a low-fat diet.

Carbs and Your Gut Bacteria

Carbs also have an influence on your gut bacteria, which may affect your weight. According to a study published in Current Obesity Report in 2015, people who are obese are more likely to have bacteria known as Firmicutes in their intestines than people who are at a healthy weight. The study researchers noted that this type of bacteria may actually cause you to absorb more calories from the food you eat.

On the other hand, people with more Bacteroidetes bacteria in their gut tend to be thinner. The Firmicutes bacteria (the kind that promote weight gain) tend to grow more in diets high in sugar and processed carbohydrates, while the Bacteroidetes bacteria (the good guys) prefer a low-carb diet.

The "Carb Coma"

Although it may not cause weight gain directly, there's also the issue of a "carb coma." This is when you've eaten a high-carb meal (let's say that you had pasta, breadsticks, a soft drink and frozen yogurt for dessert), and then very soon afterward, you find yourself sleepy, mentally foggy and a little grumpy and out-of-sorts.

You'd originally had plans to go for a walk after dinner, but now you just don't have the energy. Instead, you opt to curl up in the recliner, watching Netflix and absently munching on more carbs. What happened? Your body quickly digested all those simple carbs, resulting in a spike in blood sugar, followed by a crash, and the crash led to a depletion of energy.

You may routinely put yourself into a carb coma by eating meals that are virtually all simple carbohydrates, and in doing so, you reduce your energy levels and become more sedentary. This decrease in activity may leads to weight gain, especially in the waist area.

Target for Daily Carb Intake

The carbohydrate sweet spot varies greatly from person to person, so there's no hard answer to how many carbs you need to lose weight. A low-carb diet falls somewhere between 20 to 60 grams of carbs daily, depending on your calorie needs. The ketogenic diet, which is a very strict low-carbohydrate diet, restricts carbs to 20 to 50 grams, at most.

When you're trying to lose weight, you'll have to experiment with different low-carb plans between 20 and 60 grams of carbs to figure out which works best for you and your body. When you find your perfect carbohydrate allotment, you'll experience a boost in energy, reduced appetite, stable blood sugar levels and weight loss.

When counting your carbohydrate intake, you want to consider net carbs or the grams of carbs minus the grams of fiber. So even though foods like beans are relatively high in carbohydrates, they are also high in fiber, so the net carb amount is moderate.

Think Quality, Not Just Quantity

In addition to thinking about the quantity of carbs you're eating, you also need to think about their quality. Carbs that are high in fiber are absorbed slower than carbs that don't have as much fiber, so they don't affect your blood sugar levels as much.

With high-fiber carbs, you feel full quickly, and since they take a long time to digest once they're in your system, you don't get hungry as quickly after a meal. High fiber foods also promote a healthier balance of gut bacteria.

Include High-Fiber Foods

You'll find high levels of fiber in beans and peas, foods that are also good protein choices. Other high-fiber carbs include:

  • Lentils
  • Brown rice
  • Quinoa
  • Sweet potatoes
  • Beets
  • Fruits
  • Other vegetables

Get Your Fruits and Veggies

Although these foods contain carbohydrates, they're also packed with vitamins and other nutrients and they are relatively low-calorie. Some low-carb (and low-calorie) veggies that also have anti-inflammatory properties include:

  • Leafy greens, like spinach, kale, lettuce, turnip greens and cabbage
  • Brussels sprouts
  • Zucchini
  • Broccoli
  • Yellow squash

Berries, including blackberries, blueberries, strawberries and raspberries are the lowest carb fruit, and they're also high in fiber, antioxidants and other vitamins and minerals. Other low-carb fruits include starfruit, avocado and tomatoes.

Avoid Added Sugar

Avoid added sugar as much as you can and strictly limit or eliminate all processed carbs, like foods made with white flour (pizza, pasta, bread, muffins, cakes and cookies) and white rice. Also, eliminate sweetened drinks.

If you concentrate on eating moderate amounts of healthier, high-fiber carbs, and eliminate unhealthy, processed carbs from your diet, you may find you don't even have to worry about counting carbs. You'll just naturally lose weight by focusing on the healthy and limiting the unhealthy.

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