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Artificial Sweeteners Make You Fat

This is Part 3 in a 4-part series on Sugar and Other Sweeteners.

(1) Sugar Is Toxic: Heart Disease, Cancer & More
(2) Sugar: How Much Is Too Much?
(3) Artificial Sweeteners Make You Fat
(4) Sugar: Physical Addiction or Emotional Craving?

People drink diet soda to avoid calories and keep from getting fat. Yet study after study shows that daily use of artificial sweeteners is strongly associated with obesity. Do overweight people tend to drink diet soda, or does diet soda cause people to become overweight?

A number of recent studies make it clear: artificial sweeteners cause obesity. They confuse the body, causing appetite to increase and metabolism to slow. When something tastes like it should have calories but does not, you eat more and get fatter from what you eat. The same effect has been found with fat substitutes.

You can’t get something for nothing. Everything you consume has a cost. It’s ironic that the cost, in this case, is obesity.

Two Longitudinal Studies of Diet Soda

Two large longitudinal studies were recently completed. They showed that people who drank diet soda every day were much more likely to become overweight or obese, and to develop metabolic syndrome and type 2 diabetes. Metabolic syndrome increases the risk of cardiovascular disease and type 2 diabetes, and is associated with obesity.

In August 2008, Sharon P. Fowler and associates published a 9-year longitudinal study, covering 1979-1988, on the relationship between artificially sweetened beverages and obesity. They found that drinking more than 21 diet sodas per week was associated with almost double the risk of being overweight or obese, regardless of the baseline BMI. So even if people didn’t start off fat, if they drank more than 21 diet sodas per week, they were twice as likely to become fat by the end of the study.

In January 2009, Jennifer Nettleton and associates published a 7-year longitudinal study, covering 2000-2007, tracking diet soda consumption, type 2 diabetes, and metabolic syndrome in over 6800 people aged 45-84. Metabolic syndrome was defined using National Cholesterol Education Program Adult Treatment Panel III criteria, which requires at least three of the following:

  • Central obesity: waist circumference > 40 inches (male), > 35 inches (female)
  • Triglycerides ≥ 150 mg/dl
  • HDL Cholesterol < 40 mg/dL (male), < 50 mg/dL (female)
  • Blood pressure ≥ 130/85 mmHg (or treated with medication)
  • Fasting plasma glucose (blood sugar) ≥ 110 mg/dl (or treated with medication)

Those consuming 1 or more diet sodas per day had a 36% higher risk of metabolic syndrome than non-consumers, and a 67% higher risk of type 2 diabetes. This wasn’t due to a particular artificial sweetener since the artificial sweetener used changed over the 7-year period.

These longitudinal studies strongly suggest that artificial sweeteners cause obesity, but only controlled lab studies can offer proof. Finally we have this.

Artificial Sweeteners Confuse the Body

Susan Swithers and Terry Davidson, psychologists at Purdue University, have done a series of controlled studies that show that animals (like rats and humans) appear to use sweet taste to predict the caloric contents of food. Eating sweet noncaloric substances degrades this predictive relationship, leading to increased food intake and lowered metabolism.

In a 2008 study [PDF], some rats were given yogurt sweetened with saccharin, and some were given yogurt sweetened with glucose. Those given the artificially sweetened yogurt ate more food, gained more weight, and gained more body fat. Two changes accounted for this:

  1. Their caloric compensation ability was reduced. That is, they were less able to adjust for excess calories by reducing intake at a later time.
  2. They showed a "blunted thermic response" to sweet-tasting diets. When you are about to eat, the look and the smell of the food causes your metabolism to speed up, and this is measurable as an increase in body temperature – the "thermic response". When the rats used to artificial sweeteners ate sweet foods, their metabolisms didn’t rev up as much. The artificial sweeteners had taught the rats that sweet foods have no calories, so eating naturally sweetened food caused greater than normal weight gain.

These results were reproduced and extended in a 2009 study. In addition to saccharine and low-fat yogurt, the rats were given acesulfame potassium as the artificial sweetener and refried beans as the food. The researchers chose refried beans because they have about the same calories as low-fat yogurt, but a different nutritional profile. The previous results held, plus the researchers found that the effects were resistant to reversal. The rats given the artificial sweeteners continued to gain weight after the artificial sweetener was withdrawn.

Note that weight gain would be expected with any no-calorie sweetener used daily, even a natural one like stevia. Stevia doesn’t have the chemical risks of an artificial sweetener, but it confuses the body in the same way. Coca Cola markets a stevia-based sweetener called Truvia, and PepsiCo markets one called PureVia. They are both starting to use them in soft drinks. Beware. They will make you just as fat as artificial sweeteners, despite being more natural. (Neither is completely natural; both contain other ingredients.)

This unexpected effect of no-calorie sweeteners is probably the answer to another mystery. Generally people lose weight quickly on low-carb diets (if they can stick to them), but occasionally they don’t lose weight at all. I suspect that when they don’t, it’s because they’re using no-calorie sweeteners on a daily basis.

On the plus side, it appears that low-carb diets are more restrictive than they need to be. With the new research on fructose, there is speculation that low-carb diets only work because they reduce added sugar. Starch breaks down only to glucose, and so should not harm health or cause obesity – especially not starch that contains the original fiber, such as whole grain. This is Robert Lustig’s view [VIDEO], and for what it’s worth (sample of 1), it’s my experience. I gain weight from sugar, but not from starch. (Note that commercial bread contains sugar – if you want sugar-free bread, you’ll need to start baking.)

Try to Wean Yourself Off Sweetened Beverages

One of the most unfortunate habits you can get into is drinking sweetened beverages in place of water. Studies show that the body doesn’t know how to compensate for liquid calories. If you drink 600 calories of sweetened beverages, you don’t then eat less food. The body seems to assume that liquid intake is water and calorie-free. Also, as we saw in Part 1, sugared beverages are especially fattening – even more so than solid desserts – because they hit the liver so quickly.

Fruit juice is not a healthy alternative. As a beverage, it’s as bad for you as sugared soda. When you mix it with tea or seltzer, it’s no different from adding sugar. See Part 1 for why.

Unfortunately, artificially sweetened beverages are not a solution because they make you gain weight for a different reason.

There really is no way that you can get away with a sweetened beverage habit without gaining weight. So if you’d like to lose weight without dieting, weaning yourself off sweetened beverages is a surprisingly effective way to do it. It’s one of the single healthiest changes you can make to your eating habits. Sweetened beverages are just a habit – you can do this. It’s in your DNA to like water. I mainly drink water or seltzer, and I prefer unsweetened tea and coffee. I drink herbal tea plain, and put milk in black tea or coffee to break the acid. You might think you couldn’t possibly get used to this, but you can, and I really encourage you to try.

In the final article in this series, Part 4, I’ll talk about sugar addiction – why going without sugar for even a day (or giving up sweetened beverages) can feel so impossible. Are the cravings physical, emotional, or both, and how do you break free?

Thoughts? Comments? I’d love to hear them.