People are fatter and sicker than ever before.

Obesity rates have tripled since 1980 and have increased particularly fast in children.

The reason why this has happened is still debated among scientists, but it must be due to changes in the environment because our genes don’t change this quickly.

This article contains graphs with historical trends and results from obesity studies, showing some of the main reasons why obesity has become such a massive problem.

Here are 12 graphs that show why people get fat.

1. People Are Eating More Junk Food Than Ever

Dr. Stephan Guyenet. Fast Food, Weight Gain and Insulin Resistance. Whole Health Source.

People are eating more calories than before… but pretty much all of the increase has come from processed foods.

In the graph above, you see how the population changed its eating habits in the past 120-130 years.

At the turn of the 20th century, people were eating mostly simple, home-cooked meals. Around 2009, about half of what people ate was fast food, or other foods away from home.

This graph actually underestimate the true change, because what people are eating at home these days is also largely based on processed foods.

2. Sugar Consumption Has Skyrocketed

Johnson RJ, et al. Potential role of sugar (fructose) in the epidemic of hypertension, obesity and the metabolic syndrome, diabetes, kidney disease, and cardiovascular disease. The American Journal of Clinical Nutrition, 2007.

Added sugar is the single worst ingredient in the modern diet.

Numerous studies show that eating excess amounts of added sugar can have harmful effects on metabolism, leading to insulin resistance, belly fat gain, high triglycerides and small, dense LDL cholesterol… to name a few (1, 2).

There is also a plethora of observational studies showing that the people who eat the most sugar are at a much greater risk of getting type 2 diabetes, heart disease and even cancer (3, 4, 5).

Sugar is also fattening, partly because it doesn’t get registered in the same way as other calories by the brain, making us eat more. It also has adverse effects on hormones related to obesity (6, 7, 8, 9).

Not surprisingly, studies show that people who eat the most sugar are at a high risk of future weight gain and obesity (10).

3. People Gain Lots of Weight During The Holidays, Which They Never Get Rid Of

Dr. Stephan Guyenet. Why do we Overeat? A Neurobiological Perspective. 2014.

Most people don’t gain weight overnight… it happens slowly, over years and decades.

But the rate is uneven throughout the year and spikes dramatically during the holidays, a time when people tend to binge on all sorts of delicious holiday foods and eat much more than their bodies need.

The problem is that sometimes people don’t lose all the weight back. They might gain 3 pounds, but only lose 2 after the holidays are over, leading to slow and steady weight gain over time (11).

In fact, a large percentage of people’s lifetime weight gain can be explained just by the 6 week holiday period.

4. The Obesity Epidemic Started When The Low-Fat Guidelines Were Published

National Center for Health Statistics (US). Health, United States, 2008: With Special Feature on the Health of Young Adults. 2009 Mar. Chartbook.

There was an epidemic of heart disease running rampant in the U.S. in the 20th century.

A lot of scientists believed fat, especially saturated fat, to be the main dietary cause of heart disease (although this has since been disproven).

This led to the birth of the low-fat diet, which aims to restrict saturated fat. Interestingly, the obesity epidemic started at almost the exact same time the low-fat guidelines first came out.

Of course, this doesn’t prove anything, because correlation doesn’t equal causation.

But it does seem likely that putting the emphasis on saturated fat, while giving processed low-fat foods high in sugar a free pass, may have contributed to negative changes in the population’s diet.

There are also massive long-term studies showing that the low-fat diet does NOT cause weight loss, and does not prevent heart disease or cancer (12, 13, 14, 15).

5. Food is Cheaper Than Ever Before

Dr. Stephan Guyenet. Why do we Overeat? A Neurobiological Perspective. 2014.

One factor that has most likely contributed to increased consumption is a lower price of food.

From the graph above, you see that food prices have dropped from 25% of disposable income to about 10% of disposable income in the past 80 years.

This seems like a good thing, but it’s important to keep in mind that real food isn’t cheap… it’s processed food.

In fact, real foods are so expensive that a lot of people can’t even afford them. In many poor neighborhoods, they don’t even offer anything but junk food, which is often subsidized by the government.

How are poor people supposed to stand a chance if the only food they can afford (and access) is highly processed junk high in sugar, refined grains and added oils?

6. People Are Drinking More Sugary Soda and Fruit Juices

Authority Nutrition

The brain is the main organ in charge of regulating our energy balance… making sure that we don’t starve and don’t accumulate excess fat.

Well, it turns out that the brain doesn’t “register” liquid sugar calories in the same way as it does solid calories (16).

So if you consume a certain number of calories from a sugary drink, then your brain doesn’t automatically make you eat fewer calories of something else instead (17).

That’s why liquid sugar calories are usually added on top of the daily calorie intake. Unfortunately, most fruit juices are no better and have similar amounts of sugar as soft drinks (18).

Studies have shown that a single daily serving of a sugar-sweetened beverage is linked to a 60.1% increased risk of obesity in children (19).

Sugar is bad… but sugar in liquid form is even worse.

7. Increased Food Variety Contributes to Overeating and Weight Gain

Dr. Stephan Guyenet. Why do we Overeat? A Neurobiological Perspective. 2014.

One factor that contributes to overeating is food variety.

The graph above shows a study where rats were split in 3 groups… one group got regular healthy chow, the second group got one type of junk food, but the third got multiple types of junk food at the same time (20).

As you can see, the rats eating one type of junk food gained more than the ones eating rat chow, but the rats eating multiple types of junk food gained the most… by far.

There is some evidence that this is true in humans as well. When we have more types of foods available, we eat more… and sometimes more than our bodies need (21).

8. People Don’t Burn as Many Calories When Working

Church TS, et al. Trends over 5 Decades in U.S. Occupation-Related Physical Activity and Their Associations with Obesity. PLoS One, 2011.

A lot of people blame obesity on decreases in physical activity, that we’re just burning fewer calories than we used to.

Although leisure time physical activity (exercise) has increased, it is also true that people now have jobs that are less physically demanding.

The graph above shows how people are now burning around 100 fewer calories per day in their jobs, which may contribute to weight gain over time.

9. People Are Eating More Vegetable Oils, Mostly From Processed Foods

Authority Nutrition

The fats we are eating have changed dramatically in the past 100 years or so.

At the beginning of the 20th century, we were eating mostly natural fats like butterand lard… but then they were replaced with margarine and vegetable oils.

Most people aren’t frying real food in vegetable oil, they are getting it from processed food. Adding these oils to the foods increases the reward and caloric value, contributing to over-consumption.

10. The Social Environment Can Strongly Affect Calorie Intake

Dr. Stephan Guyenet. Why do we Overeat? A Neurobiological Perspective. 2014.

The social environment is another factor that determines calorie intake. For example, eating in a group can dramatically increase the number of calories consumed.

According to one paper, eating a meal with several people can increase calorie intake by up to 72%, or 310 calories in a single meal (22).

There are also studies showing that people tend to eat more during weekends (23).

11. People Are Sleeping Less

Cauter EV, et al. The Impact of Sleep Deprivation on Hormones and Metabolism. Medscape, 2005.

Sleep is often overlooked when it comes to weight gain and obesity.

It is known that poor sleep has negative effects on various hormones that are related to weight gain, and can contribute to increased hunger and cravings (24, 25, 26).

In recent decades, average sleep duration has decreased by 1-2 hours per night. The reasons for this are numerous, but increased artificial lighting and electronics are likely contributors.

As it turns out, short sleep duration is one of the strongest individual risk factors for obesity. It is linked to an 89% increased risk in children, and a 55% increased risk in adults (27).

12. Increased Calorie Intake

Dr. Stephan Guyenet. Why do we Overeat? A Neurobiological Perspective. 2014.

People may argue about the causes of obesity… whether it is sugar, carbs, fat, or something else.

But one indisputable fact is that calorie consumption has increased dramatically over the past few decades (28, 29).

According to studies, this increased calorie intake is more than sufficient to explain the increases in obesity (30).

But it’s important to keep in mind that it is not some collective moral failure that drives the increased calorie intake.

All behavior is driven by the underlying biology… and the way the diet and environment have changed has altered the way our brains and hormones work.

In other words, these changes have caused malfunctions in the biological systems that are supposed to prevent us from getting fat.

This is the underlying reason for the increased calorie intake and weight gain, NOT a lack of willpower, as some people would have you believe.