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

This study assessed the change in calorie intake and average body weight from 1970 to 2000. The average child now weighs 9 lbs (4 kgs) more than in 1970, while the average adult weighs about 19 lbs (8.6 kgs) more (5Trusted Source).

When comparing the change in average weight, the calculations equated almost exactly to the increased calorie intake (5Trusted Source).

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

2. BMI Has Increased Alongside Calorie Intake
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Sources: Ogden CL, et al. Mean body weight, height, and body mass index: United States 1960-2002Trusted Source. Department of Health and Human Services, Centers for Disease Control and Prevention, National Center for Health Statistics, 2004.

Body mass index (BMI) measures the height-to-weight ratio of an individual, and is used as an indicator of obesity and disease risk (6Trusted Source, 7Trusted Source).

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

Among US 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 with the rise in calorie intake.

3. Consumption of All Macronutrients Has Increased
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Source: Ford ES, et al. Trends in energy intake among adults in the United States: findings from NHANESTrusted Source. The American Journal of Clinical Nutrition, 2013.

The debate about the cause of weight gain and the obesity epidemic is still debated. Some blame carbs, while others blame fat.

Interestingly, data from the National Health and Nutrition Examination Survey suggests that the percentage of calories from carbs, protein and fat has stayed relatively constant over the years (10Trusted Source).

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

4. Weight Loss on Low-Fat and High-Fat Diets is the Same
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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 lipidsTrusted Source. The American Journal of Clinical Nutrition, 2005.

Some researchers claim that low-carb diets provide a metabolic advantage over other diets (11Trusted Source, 12Trusted Source).

Research has shown a low-carb diet can be effective for weight loss and provide numerous health benefits, but the primary reason that it causes weight loss is still 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.

Most other studies that are isocaloric, as in when calories are controlled in both groups, show that weight loss on low-carb and low-fat diets is the same.

That being said, when people are allowed to eat until fullness, they usually lose much more fat on a very low-carb diet, because the diet suppresses appetite.

5. Weight Loss is the Same on 4 Different Calorie-Matched Diets
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Source: Sacks FM, et al. Comparison of weight-loss diets with different compositions of fat, protein, and carbohydratesTrusted Source. New England Journal of Medicine, 2009.

This study confirms some of the research above, testing four different calorie-restricted diets over a two-year period (13Trusted Source).

All four groups lost between 7.9 and 8.58 lbs (3.6 to 3.9 kgs), which is very similar. The researchers also found no differences in waist circumference between groups.

Interestingly, this study found that there was no difference in weight loss when carbs ranged from 35% to 65% of total calorie intake (13Trusted Source).

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

6. Counting Calories Helps You Lose Weight
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Source: Carels RA, et al. Can following the caloric restriction recommendations from the Dietary Guidelines for Americans help individuals lose weight?Trusted Source Eating Behaviors, 2008.

It is commonly recommended that people eat 500 fewer calories than they need in order to lose weight. This approach is commonly used in the weight loss and fitness industries.

The study above looked at the effectiveness of counting calories, and whether it helped participants lose more weight (14Trusted Source).

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 to those who did not pay close attention to calories, individuals who tracked their calorie intake lost nearly 400% more weight (14Trusted Source).

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

7. Daily Activity Levels and Calorie Expenditure Have Decreased
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Source: Levine J, et al. Non-exercise activity thermogenesis: the crouching tiger hidden dragon of societal weight gain.Trusted Source Arteriosclerosis, Thrombosis, and Vascular Biology, 2006.

Along with increased calorie intake, evidence also strongly suggests that people are less physically active than before (15Trusted Source, 16Trusted Source).

This creates what is known as an “energy gap,” or a difference between calories consumed and calories burned.

Interestingly, research shows that obese people are significantly less physically active than those who are lean.

This doesn’t just apply 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 (17Trusted Source).

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 (5Trusted Source, 16Trusted Source, 18Trusted Source).

Calories Matter, That is a Fact

The current data strongly supports the idea that increased calorie intake can account for the current obesity epidemic.

Studies also show that reducing calories causes weight loss, regardless of diet composition.

That being said, it is also true that some foods are more fattening that others.

Most whole foods tend to be very filling, but highly processed junk foods tend to make it really easy to consume large amounts of calories.

Even though food quality is very important for optimal health, total calorie intake is a key determinant of how much weight you lose.