Is sugar responsible for the obesity epidemic?

5 min read

MNU Certified Nutritionist and PT, Tony Cottenden, digs deep into the sugar debate to ask: if sugar intake is falling, why is obesity rising?

Sugar is bad news, right? It’s devoid of nutrients - pure carbs and empty calories. And it’s in everything. Surely sugar and obesity go hand in hand. It must be the  main culprit for our current problems with rising obesity levels?

Well, not quite. Increasing numbers of studies - backed by expert opinion and anecdotal evidence - strongly suggests that sugar, in fact, is not the problem at all.

So what is the cause of the obesity crisis, if not sugar?

Our long history with sugar

Sugar has only recently been cast as a scapegoat for obesity, but our relationship with the sweet stuff goes back to before records began.

Sugar’s quick-fix carbohydrate energy was highly valuable to early mankind (indeed it’s still highly valuable to modern man, when we work hard enough to need it!). Early primates probably ate a lot of fruit, just as today’s primates do. Fruit sugars are a great source of energy in the wild.

Pear Tree
Pears growing in the wild provide a great source of sugar for energy.

Once we discovered fire and invented tools, we veered away from fruits and plants and started eating more animal sources of food, plus starches that needed digging up and cooking. But our bodies still do well on sugars, especially fruits.

Is sugar making us fat?

It’s no secret that our intake of sugars has skyrocketed over the past two generations. In 1822, records show the average American ate 6.3 lbs of added sugar a year. This figure had increased to 101 lbs a year by 2004.

But does this mean sugar is at the root of our current obesity problem?

The data says no.

The CDC (Centre for Disease Control and Prevention) puts out a survey called the National Health and Nutrition Examination Survey (NHANES). It documented the USA’s “obesity epidemic” between 1978 and 1991, and again into the 2000s.

According to NHANES, US adult obesity numbers increased from 15%-33% between 1978 and 2004. But the increase in sugar consumption only went up by 17%. That’s a 17% rise in sugar, for a 120% rise in obesity? Something doesn’t add up.

Between the 1970s and 2000s, sugar wasn’t a factor in weight gain. It wasn’t even a factor in increased calorie intake.

What does the science say?

If you’re not too bothered about geeking out on the sciencey bits, move onto the end of the article where I sum it all up.

So, to the science. There are plenty of observational studies on sugar consumption and body composition/body fat. The results are a surprise - but not a one-off.  Check this out from a 1995 review paper (1):

“…We consider whether consumption of high amounts of sugars presents a public health problem by contributing to the development of obesity. Metabolic studies show that diets high in fat are more likely to result in body fat accumulation than are diets high in carbohydrates. There is no indication that simple sugars differ from complex sugars in this regard. Epidemiologic data show a clear inverse relation between intake of sugar and fat…. There is ample reason to associate high-fat diets with obesity but, at present, no reason to associate high-sugar diets with obesity.” (1)

Why would people who eat less sugar actually be more lean? Could it be because they eat less fat, and this enables them to regulate their total caloric intake?

Data from human studies

There was a pretty crazy study done in 1971 paper where subjects ate 82% of their calories from fruit for 6 months (the remaining 18% of calories were from nuts) (2).  That means fruit sugar made up a possible 65% of their diet.

“A considerable number of the normal subjects claimed that their physical condition improved while they were on the diet…. Most subjects lost weight initially (then) levelled off at figures which corresponded more or less with the calculated theoretical normal weights.” (2)

So these people maintained the “theoretical ideal” of their individual body weight on a diet of 65% carbs from fruit sugar. It’s getting more and more difficult to believe sugar is fattening. Could it actually be something to do with the many changes in our diets, eating habits, portion sizes, and the availability of hyper-palatable foods since 1971?

In 2002, a study (3) took overweight subjects with a metabolic syndrome and split them into 3 groups: one replaced 1/4 of their daily fat intake with sugary foods, another which replaced 1/4 of daily fat intake with complex carbohydrates. The third group was the control - nothing changed. None of the groups had their total calories restricted. Bear in mind, it would be reasonable to assume that people with a metabolic syndrome could be sensitive to sugar.

In 6 months, group 2 (the complex carbs people) lost 4.25. There were no significant changes in group 1 or the control group. So what do we take from this? That replacing fat content with starchy carb foods can lead to weight loss.

Can sugar ever make us fat?

It’s not as clear cut as saying sugar cannot and does not make us fat. Of course it can - but context is everything. Here's some context to consider:

  • Sugar and sugary foods are tasty! We are more likely to overeat on them than on other, less sweet foods this leads to overconsumption of total calories
  • Sugar is often found alongside fats in foods - think bakery goods, cakes, muffins, doughnuts, even things like crisps. This combination means high calories
  • Sugar isn’t very filling, at least in its pure form. It lacks fibre and protein - two of the things we know help with satiety. Again, that makes it easy to overeat on sugary foods
  • Sugary, sweet foods are hyper-palatable and often chosen for reward-type eating, which is linked with emotional eating and overeating
A bowl of sugar coated donuts are hard to resist due to being highly palatable.

OK, so high-sugar diets don't necessarily produce body fat accumulation in humans, and they can even allow body fat loss under some circumstances, but are there situations where sugar can cause fat accumulation?  The answer is an emphatic yes: when your diet combines high sugar and high fat.

The bottom line is, if you eat more calories than you burn, you will gain weight.

An expert’s advice on sugar

I’m not suggesting you go ahead and start eating 65% of your total calorie intake from fruit sugars like that 1971 study. But I would urge you to ignore the scaremongering and have your own thoughts about sugar and sugary foods, too. After all, sugar is just energy. It can be pretty useful when you need fast energy for training, long-duration activity, or even a brain boost.

The trick lies in regulating your intake, over-riding potential cravings, and keeping an eye on total energy intake (in line with your goals).

  1. Sugar is not inherently fattening - no more than any other calorie source
  2. Unrefined sugar (complex carbohydrates) is not an enemy of fat loss if calories are in check
  3. Sugar can lead to over-eating (and weight gain) if it makes the food tasty, hard to resist, or difficult to portion control
  4. Know yourself - if you struggle to stop eating sugary (or sugar-added foods) then exercise extra caution
  5. Avoid drinking your sugar. It’s very difficult to manage total calorie intake if you include sugar-sweetened drinks
  6. Fruit isn’t fattening. It’s a decent source of fibre, helps with hydration, and can be a high-volume/low energy density food choice




Tony Cottenden

Tony Cottenden

An MNU Certified Nutritionist, PTC qualified Personal Trainer and founder of Tony is passionate about helping busy adults reach their health and fitness goals.