Many dietary and lifestyle habits can lead to weight gain and cause you to put on excess body fat.

Consuming a diet high in added sugars, such as those found in sweetened beverages, candy, baked goods, and sugary cereals, is a contributing factor in weight gain and chronic health conditions, including obesity, heart disease, and diabetes (1, 2).

The ways in which added sugar intake leads to weight gain and increased body fat are complex and involve many factors.

Here are 6 reasons why added sugar is fattening.

1. High in empty calories

Added sugars are sweeteners added to foods and beverages to improved taste. Some common types include fructose, corn syrup, cane sugar, and agave.

Excess sugar may cause you to pack on weight because it’s high in calories while offering few other nutrients.

For example, 2 tablespoons (30 ml) of the common sweetener corn syrup contain 120 calories — exclusively from carbs (3).

Added sugars are often referred to as empty calories, as they’re relatively high in calories yet void of nutrients like vitamins, minerals, protein, fat, and fiber, which your body needs to function optimally (4).

Plus, foods and beverages that typically contain a lot of added sugars, such as ice cream, candy, soda, and cookies, tend to be loaded with calories as well.

Though using small amounts of added sugar is unlikely to cause weight gain, regularly indulging in foods high in added sugars may cause you to gain excess body fat quicker and more drastically.

Summary Added sugar is a source of empty calories and offers little in terms of nutrition. Foods rich in added sugars tend to be high in calories, which can cause weight gain.

2. Impacts blood sugar and hormone levels

It’s well known that eating sugary foods significantly raises your blood sugar levels.

Though enjoying a sweet food infrequently isn’t likely to harm health, daily consumption of large amounts of added sugar can lead to chronically elevated blood sugar levels.

Prolonged elevated blood sugar — known as hyperglycemia — can cause serious harm to your body, including weight gain (5).

One way hyperglycemia leads to weight gain is through promoting insulin resistance.

Insulin is a hormone produced by your pancreas that moves sugar from your blood into cells, where it can be used for energy. Insulin is also involved in energy storage, telling your cells when to store energy as either fat or glycogen, the storage form of glucose.

Insulin resistance is when your cells stop responding properly to insulin, which leads to elevated sugar and insulin levels.

High blood sugar levels impair normal cell function and promote inflammation, which increases insulin resistance, furthering this destructive cycle (6, 7).

Though cells become resistant to insulin’s effect on blood sugar uptake, they remain responsive to the hormone’s role in fat storing, meaning that fat storage is increased. This phenomenon is known as selective insulin resistance (8, 9).

This is why insulin resistance and high blood sugar are associated with increased body fat — specifically in the belly area (10, 11).

Additionally, high blood sugar levels and insulin resistance interfere with leptin, a hormone that plays a major role in energy regulation — including calorie intake and burning — and fat storage. Leptin decreases hunger and helps reduce food intake (12).

Likewise, high-sugar diets are associated with leptin resistance, which increases appetite and contributes to weight gain and excess body fat (13).

Summary High-sugar diets contribute to prolonged elevated blood sugar, insulin resistance, and leptin resistance — all of which are linked to weight gain and excess body fat.

3. Foods high in added sugar tend to be less filling

Foods and beverages that are packed with added sugar, such as cakes, cookies, ice cream, candy, and soda, tend to be low in or completely lacking in protein, a nutrient essential for blood sugar control that promotes feelings of fullness.

In fact, protein is the most filling macronutrient. It does this by slowing digestion, keeping blood sugar levels stable, and regulating hunger hormones (14).

For example, protein helps reduce levels of ghrelin, a hormone that drives appetite and increases calorie intake (15).

Conversely, eating protein stimulates the production of peptide YY (PYY) and glucagon-like peptide 1 (GLP-1), hormones associated with feelings of fullness that help reduce food intake (15).

Eating foods rich in carbs — particularly refined carbs high in added sugars — yet low in protein can negatively impact fullness and may lead to weight gain by causing you to eat more at subsequent meals throughout the day (16, 17, 18).

High-sugar foods also tend to be low in fiber, a nutrient that can increase feelings of fullness and reduce appetite — though not as much as protein (19).

Summary High-sugar foods and beverages are generally low in protein and fiber, nutrients that are essential for keeping you feeling full and satisfied.

4. Displaces healthy foods

If most of your diet revolves around foods high in added sugars, chances are you’re missing out on important nutrients.

Protein, healthy fats, fiber, vitamins, and minerals are all nutrients found in whole, nutritious foods that your body needs to function optimally and stay healthy. They’re usually lacking in sugary products.

Additionally, refined foods and beverages that are high in added sugar don’t have beneficial compounds like antioxidants, which are concentrated in foods like olive oil, nuts, beans, egg yolks, and brightly colored vegetables and fruits (20, 21).

Antioxidants help protect your cells from damage caused by highly reactive molecules called free radicals.

Oxidative stress — an imbalance between antioxidants and free radicals — has been linked to a variety of chronic conditions, such as heart disease and certain cancers (22).

Unsurprisingly, diets high in added sugars increase your risk of the same chronic diseases linked to oxidative stress, as well as your risk of obesity and weight gain (1, 23, 24, 25, 26).

Eating foods high in added sugar displaces nutrient-rich, healthy foods like vegetables, fruits, proteins, and healthy fats — which could negatively impact your weight and overall health.

Summary Added sugars displace healthy foods, may lead to weight gain, and increase your risk of chronic health conditions like heart disease.

5. May cause you to overeat

Eating too much added sugar — particularly foods rich in a type of sugar called fructose — can significantly increase levels of the hunger-promoting hormone ghrelin while decreasing levels of the appetite-suppressing hormone peptide YY (PYY) (27).

Fructose may also increase appetite by affecting a part of your brain called the hypothalamus. The hypothalamus is responsible for many functions, including appetite regulation, calories burned, as well as carb and fat metabolism (28).

Animal studies indicate that fructose impacts signaling systems in your hypothalamus, increasing levels of hunger-stimulating neuropeptides — molecules that communicate with one another, influencing brain activity — while decreasing fullness signals (29).

What’s more, your body is predisposed to crave sweetness. In fact, research shows that sugar consumption is driven by the pleasure derived from the sweet taste of sugary drinks and foods.

Studies suggest that sweet-tasting foods activate certain parts of your brain that are responsible for pleasure and reward, which may enhance your craving for sweet food (30, 31).

Additionally, sugar may increase your desire for highly palatable, calorie-rich foods.

A study in 19 people found that consuming 10 ounces (300 ml) of a sugary drink led to an increased response to pictures of high-calorie, palatable foods like cookies and pizza and reduced levels of the appetite-suppressing hormone GLP-1, compared to a placebo (32).

Thus, the impact of sugar on hormones and brain activity may increase your desire for sweet-tasting foods and may encourage overeating — which can lead to weight gain (33).

Summary Sugar affects appetite-regulating hormones and reward centers in your brain, which may increase the desire for highly palatable foods and cause you to overeat.

6. Linked to obesity and chronic disease

Numerous studies have linked high intake of added sugars to weight gain and chronic conditions, such as obesity, heart disease, and diabetes.

This effect has been seen in both adults and children.

A recent review of 30 studies in more than 242,000 adults and children found a significant association between sugar-sweetened beverages and obesity (34).

Countless studies link sugary foods and beverages to weight gain in different populations, including pregnant women and teens (35, 36, 37).

Another study in 6,929 children demonstrated that those between the ages of 6 and 10 who consumed more added sugars had significantly more body fat than children who consumed less added sugar (38).

Studies show that diets high in added sugar can increase your risk of chronic health conditions as well.

In a population study in more than 85,000 people, the risk of dying from heart disease was more than twice as high in those consuming 25% or more of their daily calories from added sugars, compared to those who consumed less than 10% of calories from added sugar (39).

What’s more, added sugar is strongly associated with an increase in heart disease in children through its role in raising body fat, cholesterol, and triglyceride levels — all significant risk factors for heart disease (40).

Sugar-sweetened beverages are also associated with the development of type 2 diabetes in adults (41, 42, 43).

Plus, added sugar consumption may increase your risk of depression, a condition that may promote weight gain (44, 45).

Summary Consuming too much added sugar can cause weight gain and significantly increase your risk of chronic conditions like obesity, heart disease, and diabetes.

The bottom line

Interfering with your hormones, increasing hunger, and displacing healthy foods are just a few of the ways that added sugars can lead to weight gain.

Aside from causing you to put on excess body fat, eating too much added sugar can significantly increase your risk of chronic conditions, such as obesity, heart disease, and diabetes.

If you want to reduce added sugars in your diet to avoid weight gain and improve your overall health, try out a few of the simple tips listed in this article to help kick your sugar habit for good.