Obesity rates have risen in recent decades.

In 2012, over 66% of the U.S. population had either overweight or obesity (1).

While macronutrients, food types, and other factors can play a role, an energy imbalance is often a major contributor (2, 3, 4).

If you eat more calories than you need for energy, weight gain can result.

Here are 7 graphs that show that calories matter.

Source: Swinburn B, et al. Increased food energy supply is more than sufficient to explain the US epidemic of obesity. The American Journal of Clinical Nutrition, 2009.

This study assessed changes in calorie intake and average body weight from 1970 to 2000. It found that in 2000 the average child weighed 9 pounds (4 kgs) more than in 1970, while the average adult weighed about 19 pounds (8.6 kgs) more (5).

The researchers found that the change in average weight equated almost exactly to the increase in calorie intake.

The study showed that children now consume an additional 350 calories per day, while adults consume an additional 500 calories per day.

Sources: Ogden CL, et al. Mean body weight, height, and body mass index: United States 1960-2002. Department of Health and Human Services, Centers for Disease Control and Prevention, National Center for Health Statistics, 2004.

Body mass index (BMI) measures your height-to-weight ratio. It can be an indicator of obesity and disease risk (6, 7).

In the last 50 years, the average BMI has risen 3 points, from 25 to 28 (8).

Among U.S. adults, each 100-calorie increase in daily food intake is associated with a 0.62-point increase in average BMI (9).

As you can see in the graph, this rise in BMI correlates almost exactly to the rise in calorie intake.

Source: Ford ES, et al. Trends in energy intake among adults in the United States: findings from NHANES. The American Journal of Clinical Nutrition, 2013.

Some people believe carbs lead to weight gain, while others think that fat is the cause.

Data from the National Health and Nutrition Examination Survey suggests that the percentage of calories from macronutrients — carbs, protein, and fat — has stayed relatively constant over the years (10).

As a percentage of calories, carb intake has increased slightly, while fat intake has decreased. However, the total intake of all three macronutrients has gone up.

Source: Luscombe-Marsh ND, et al. Carbohydrate-restricted diets high in either monounsaturated fat or protein are equally effective at promoting fat loss and improving blood lipids. The American Journal of Clinical Nutrition, 2005.

Some researchers claim that low carb diets are more likely to boost metabolism than other diets (11, 12).

Research has shown a low carb diet can be effective for weight loss and provide numerous health benefits. However, the main reason it causes weight loss is calorie reduction.

One study compared a low fat diet to a high fat diet during 12 weeks of calorie restriction. All meal plans restricted calories by 30%.

As the graph shows, there was no significant difference between the two diets when calories were strictly controlled.

Furthermore, most other studies that have controlled calories have observed that weight loss is the same on both low carb and low fat diets.

That said, when people are allowed to eat until they feel full, they usually lose more fat on a very low carb diet, as the diet suppresses appetite.

Source: Sacks FM, et al. Comparison of weight-loss diets with different compositions of fat, protein, and carbohydrates. New England Journal of Medicine, 2009.

This study tested four different calorie-restricted diets over 2 years and confirms some of the research above (13).

All four groups lost 7.9–8.6 pounds (3.6–3.9 kgs). The researchers also found no differences in waist circumference between groups.

Interestingly, the study found that there was no difference in weight loss when carbs ranged from 35–65% of total calorie intake.

This study demonstrates the benefits of a reduced-calorie diet on weight loss, regardless of the diet's macronutrient breakdown.

Source: Carels RA, et al. Can following the caloric restriction recommendations from the Dietary Guidelines for Americans help individuals lose weight? Eating Behaviors, 2008.

To lose weight, many experts recommend eating 500 fewer calories than you need.

The study above looked at whether counting calories helped people lose more weight (14).

As you can see in the graph, there was a strong correlation between the number of days participants tracked calorie intake and the amount of weight they lost.

Compared with those who did not pay close attention to calories, those who tracked their calorie intake lost nearly 400% more weight.

This shows the benefits of monitoring your calorie intake. Awareness of your eating habits and calorie intake affects long-term weight loss.

Source: Levine J, et al. Non-exercise activity thermogenesis: the crouching tiger hidden dragon of societal weight gain. Arteriosclerosis, Thrombosis, and Vascular Biology, 2006.

Along with increased calorie intake, evidence suggests that people are less physically active than before, on average (15, 16).

This creates an energy gap, which is a term that refers to the difference between the number of calories you consume and burn.

There is also evidence that, overall, people with obesity may be less physically active than those who do not have obesity.

This not only applies to formal exercise but also non-exercise activity such as standing. One study found that lean people stood for about 152 minutes longer each day than people with obesity (17).

The researchers concluded that if those with obesity were to match the lean group's activity levels, they could burn an additional 350 calories per day.

This and other studies suggest that a reduction in physical activity is also a primary driver of weight gain and obesity, along with increased calorie intake (5, 16, 18).

The current evidence strongly supports the idea that a higher calorie intake can lead to weight gain.

While some foods may be more fattening than others, studies show that, on the whole, reducing calories causes weight loss, regardless of diet composition.

For example, whole foods may be high in calories, but they tend to be filling. Meanwhile, highly processed foods are easy to digest, and after eating a meal, you will soon feel hungry again. In this way, it becomes easy to consume more calories than you need.

While food quality is essential for optimal health, total calorie intake plays a key role in gaining and losing weight.