The surprising truth about sugar.

Here’s everything you need to know about what it does to your body.


Worried you’re eating too much sugar? Wondering how much is safe to eat? Or whether it’s bad for you… no matter what? It’s time we took a clear-headed look at this topic. It’s time you heard the truth about sugar.

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Is sugar “good”?

Is sugar “bad”?

It’s hard to know for sure these days.

Which is interesting because…

Sugar is a fundamental molecule in biology.

Human bodies need sugar.

Sugar makes up the backbone of our DNA. Helps power our cells. Helps store energy for later. Plants convert sunlight into sugar. We convert sugar into fuel.

Molecules like glucose and fructose (just two of the many types of sugar) are so basic to our biological needs, even bacteria love them.

Indeed, sugar’s the breakfast of champions, chemically speaking.

Yet, somewhere along the way, sugar became the bad guy.

Why did we start hating on sugar?

When did we start wanting to purge it from our bodies?

Why do some of us fear it so much?

At this point… do we just need a little relationship counseling?

Or is it a toxic relationship?

Is it time to part ways?

The truth is, this is a difficult conversation to have because…

Almost all of us are emotionally invested in our position on sugar.

Talking about it brings up a lot of controversy and intense debate, even among scientists who are supposed to be “objective”.

So why not step back and take a fresh look?

In this article, we’ll explore five key questions about sugar:

Does sugar cause obesity?Does sugar cause us to gain weight / fat?Does sugar cause diabetes?Does sugar cause cardiovascular disease?How much sugar is OK to eat?

Yes, we’re biased too.

At Precision Nutrition, we generally consider ourselves ‘nutritional agnostics’. (Case in point: our view on the absolute best diet.)

We help people become their healthiest, fittest, strongest selves — in a way that works for their unique lives and bodies.

In our work with over 100,000 clients clients, we’ve learned a few things…

… that one size doesn’t fit all,

… that an all-or-nothing approach doesn’t work for most people,

… that fitness and health habits should be doable on your worst day, not just your best.

So here’s our bias in this article.

We follow the complexities of nutrition evidence as best we can, always interpreting them through the lens of:

How does practice X or Y work for us, for the clients we coach, and for the fitness professionals we certify?Does said practice help us make our food choices wiser, saner, and simpler?Does it address individual differences between people?(And if not, how can we help adapt each person’s diet to match their unique needs?)

You can ask yourself these same questions as you go through the article. And, of course, feel free to come to your own conclusions.

But first, let’s get to know our sugars.

What is sugar?

Most of us think of “sugar” as the white stuff we put in coffee, or maybe what makes up 90% of those colored marshmallow cereals.

However, “sugar” is actually a group of molecules that share a similar structure. So we might actually call them “sugars”, plural.

This group includes lots of members such as:

glucosefructosesucrose, aka table sugar (which is glucose + fructose)maltose (which is glucose + glucose)galactoselactose (galactose + glucose, found in dairy)

And so on.

Sugars naturally occur in biology and in most foods (even if just in trace amounts). For example, here’s what the breakdown of sugars looks like in a banana:

There is, of course, much more sugar in processed and refined foods than in less-processed and unrefined foods.

(We’ll come back to this important point in a moment.)

Sugars live under the larger umbrella of “carbohydrates”.

Along with the sweet stuff, this macronutrient group also includes:

starches (like in potatoes or rice),fiber (like the husks of whole grains), andstructural building blocks like chitin (which makes up the shells of crustaceans) or cellulose (which makes up things like the trunks of trees).

The more complex the molecule, the slower it digests.

Sugars, which are simpler, digest more quickly.Starches and fiber, which are bigger, more complicated molecules, digest more slowly, if at all. (This is why eating more fiber can help us feel fuller, longer.)

Most carbohydrates are actually broken down into simpler sugars once they’re digested.

Other carbohydrates (such as insoluble fiber) don’t really get broken down nor absorbed fully, although our intestinal bacteria often love munching on them.

So: Sugars are a type of carbohydrate, but not all carbohydrates are sugars. And some carbohydrates break down quickly/easily into sugars. Others don’t.

This point is important to understand, because it tells us that not all carbohydrates do exactly the same things in our bodies.

Evolution has helpfully given us the ability to “taste” sugar.

Sugar-type molecules react with receptors on our tongue, which then tell our brain “OM NOM NOM DELICIOUS!”

Sugar tastes good to us, because in nature, sweet foods like fruits are often full of good stuff like vitamins, minerals, and energy.

But we differ in our physiology and behavior.

In all things, humans are diverse and variable.

Some of us like and seek out sugar more than others. This may be genetic. Or we may have learned it as we grew up. Or both.

For example, some of us like sugar in small doses; we can only eat a little before pushing the dessert plate away. While others like it a lot; the more we eat the more we want. The idea of “too much sugar” doesn’t compute.

Likewise, some of our bodies seem better suited to sugar than others.

For example, some of us can eat sugar all day long and feel fine. While others can only tolerate a little bit before our pancreas (which secretes insulin, a hormone that helps sugar get into the cells) tells us to knock it off.

In general, most of us like at least some sweetness.

When we’re young, we tend to like sweetness more and avoid bitter foods more. Yet each person’s response to sugar and sweet taste is unique.

With that said, let’s get back to the questions at hand. Starting with…

Question #1: Does sugar cause obesity?

The term “obese” (or “overweight”) is, like sugar, a contentious thing. In this article we’ll use it just for the purpose of discussion, so bear with us.

The World Health Organization defines “obese” as having a Body Mass Index higher than 30. Of course, some fit athletes (like heavyweight boxers or rugby players) might have a higher BMI but still have a low body fat percentage.

However, for most folks, having a BMI higher than 30 signifies that they have a higher-than-average level of body fat. 

(Indeed, some studies that correlate BMI with body fat testing suggest that BMI may even under-estimate how much body fat a person has.)

When it comes to obesity, there have always been people who are heavier, and/or who have more body fat, than most other folks like them.

However, over the last several decades, “average people” in industrialized countries have gotten heavier, bigger, and gained more body fat fairly rapidly.

It’s now statistically “normal”.

Although this shift is happening worldwide, and there are differences by ethnic group and socioeconomic class, it’s particularly noticeable as a general trend in the United States.

Along with body weights, we can look at changes in body fat percentage and overall fitness levels. Here, we also see that over time, body fat percentage has gone up, and fitness levels have gone down.

Currently in the United States, the average body fat percentage for men is around 28%, and the average for women is around 40%.

For comparison:

In general, 11-22% for men, and between 22-33% body fat for women, is considered a “healthy” range.Lower than that is still “healthy” (to a point), but generally considered “athletic” or “lean”.

Does increased sugar consumption explain body weight trends?

Could sugar be responsible for changing body weights and body compositions in industrialized countries?

By reviewing data from the USDA Economic Research Service, National Health and Nutrition Examination Surveys (NHANES), as well as Food Frequency Questionnaires from the long-running Framingham Heart Study, we can track food intake from multiple angles. These varying streams of data all show fairly consistent trends.

They tell us that, since 1980, Americans:

Continued to eat the same total amount of fat. (Though they generally ate less naturally-occurring fats, like in whole fat dairy, and ate more added fats, like oils.)Ate more carbohydrates. (Especially refined ones that included added sugars.)

So, as a percent of total calories consumed, fat dropped. But we didn’t end up eating less fat. We just added more sugar and other carbs on top of the fat we were already eating.

This added up to approximately 200-400 extra calories per day.

In terms of calories, that’s like eating an extra McDonald’s hamburger or a double cheeseburger, on top of your existing meals, every day.

Whether those calories came from sugar is probably irrelevant.

This increased energy intake alone, combined with decreasing rates of daily physical activity, is probably enough to explain people getting heavier.

Yes, but how might sugar play a role?

We can’t say that sugar specifically was the culprit behind the obesity surge for everyone. (Remember, humans vary.)

But our increased sugar consumption does seem to correlate with continued obesity levels… up until recently.

For about four hundred years, human beings have been enjoying more and more sugar.

Once Europeans discovered tropical trading routes and set up cheap slave labor economies to raise sugar cane, sugar became more and more available to the average person.

Indeed, sugar quickly became the food of the poor.

(It was said that the entire working class of the British Isles lived on jam and sugared tea during the Industrial Revolution.)

As a prime colonial power, the British once claimed the title of biggest sugar consumers. Per year, the average Brit consumed:

4 lbs (1.8 kg) in 1704.18 lbs (8.2 kg) in 1800.90 lbs (40.8 kg) in 1901.

However, once they got rolling as a country, Americans weren’t far behind. Per year, the average American consumed:

6 lbs (2.7 kg) of sugar in 1822.40 lbs (18.1 kg) in 1900.90 lbs (40.8 kg) by the 1920s.There was a subsequent drop due to the Great Recession & World War II.90 lbs per person again by the 1980s.

Then they really took off: By 1999, the US reached peak sugar consumption of nearly 108 lbs (49 kg) of sugar per person per year.

Between 1980-1999 Americans ate more sugar. And obesity rates got higher.

But then something changed: Our sugar consumption actually started to decrease.

Interestingly, since 1999 through 2013 (most recent data available) intake of added sugar has actually declined by 18% (or as much as 22%, depending on the data).

This drop has brought Americans’ current added sugar intake back down to 1987 levels.

And during this time, total carbohydrate intake has dropped as well. (Makes sense, as this was the dawn of the low-carb phenomenon.)

Nevertheless, though sugar and carb intake have declined over those 14 years, adult obesity has continued to climb — from 31% of the American population in 1999, to 38% as of 2013.

(Diabetes diagnoses have continued to climb as well, which we’ll address in a moment.)

So, despite lowering sugar intake by nearly 20% over a 14 year period, obesity (and diabetes) rates have continued to climb.

Along with sex, ethnic, and socioeconomic differences in obesity rates, this suggests that changing body sizes and compositions is probably a complex, multi-factored phenomenon.

Bottom line here: No single thing — including sugar — causes obesity.

Many factors work together to contribute to a consistent energy (calorie) surplus, which ultimately leads to fat gain. One of those things is often sugar, but not always, and not alone.

Question #2: Does sugar cause us to gain weight / fat?

So, we can’t unequivocally blame sugar for increased obesity rates.

But many of us are still wondering whether sugar is a gateway to fat gain.

It seems logical. Carb and sugar consumption are the main drivers of insulin release. Insulin’s job is to help store nutrients, including fat.

Therefore, it seems obvious. Carbs and sugar cause fat gain, right?

Once again, our scientist friends reveal that it’s a bit more complicated than that. Let’s take a look at a couple of studies that explore this question.

Study 1: How do carbs, sugar, and/or insulin release affect body fat?

In 2015, a small pilot study was conducted by Dr. Kevin Hall to investigate the carb/sugar/insulin model of obesity.

What happens if we keep calories and protein the same, but play with dietary sugar and fat levels?

Here’s how the study worked.

19 participants had to live in a metabolic ward, where the researchers controlled virtually everything about how they lived, what they ate, etc.The participants tried both lowe