That Diet Soda is Making You FAT

You see it all the time, a person who wants to lose weight opts for a diet soda instead of one loaded with high fructose corn syrup - that way they get the same basic taste with none of the calories. It makes perfect sense. Unfortunately, research has consistently shown that people who consume diet drinks are actually more likely to gain weight [1].

So how can a beverage with zero calories make you fat?

It all comes down to the way artificial sweeteners disrupt the body's ability to regulate caloric intake. When real foods are consumed, the digestive tract signals the brain to release chemicals that make us feel full. Artificial sweeteners do not signal the brain to release these chemicals, which means we either stay hungry or, as research has shown, actually get hungrier.

To make matters worse, artificial sweeteners negatively alter the normal balance of insulin and leptin, hormones that affect the body's ability to maintain normal weight. This eventually makes the body resistant to these important hormones, resulting in reduced energy metabolism and fewer calories being burned.

So on the one hand we have diet soda encouraging insulin and leptin resistance, which means the body will stop recognizing signals to burn fat or stop eating, and on the other hand it's not triggering the proper brain signals to keep us from eating more.

Zero calories or not, diet soda is a recipe for gaining weight.

The Details
Studies examining the effects of artificial sweeteners have demonstrated a link between diet drinks and weight gain. An analysis of the medical literature on this topic was recently reported in the June 2010 issue of the Yale Journal of Biology and Medicine, with a number of interesting findings about artificial sweeteners and weight.

First, the San Antonio Heart Study examined 3,682 adults over a seven- to eight-year period in the 1980s with the following results:

"When matched for initial body mass index (BMI), gender, ethnicity, and diet, drinkers of artificially sweetened beverages consistently had higher BMIs at the follow-up, with dose dependence on the amount of consumption. Average BMI gain was +1.01 kg/m2 for control and 1.78 kg/m2 for people in the third quartile for artificially sweetened beverage consumption." [1]

The American Cancer Society also did a study in the 1980s where they examined 78,694 women who were highly homogenous with regard to ethnicity, age, and socioeconomic status. It found that:

"At one-year follow-up, 2.7 percent to 7.1 percent more regular artificial sweetener users gained weight compared to non-users matched by initial weight. The difference in the amount gained between the two groups was less than two pounds, albeit statistically significant." [2]

As you can see, while there aren't huge differences in overall weight gain, the important takeaway is that diet soda drinkers are actually gaining more weight than regular soda drinkers. The question is "Why?"

Apparently, these artificial sweeteners may be fooling our taste buds, but they're not fooling our bodies.

"Unlike glucose or sucrose, which decreased the energy intake at the test meal, artificial sweetener preloads either had no effect [3,4] or increased subsequent energy intake [5,6]. Those findings suggest that the calories contained in natural sweeteners may trigger a response to keep the overall energy consumption constant."

In other words, although you may be consuming zero calories now, your body will convince you to get those calories later.

One might logically assume that psychology plays a part in the decision to eat more later, but the results were the same when this issue was studied in rats.

"Rats conditioned with saccharin supplement had significantly elevated total energy intake and gained more weight with increased body adiposity compared to controls conditioned with glucose." [7]

It's safe to say that these rats weren't thinking "Well, I had that diet soda earlier so I guess a few more chips couldn't hurt." Rats operate on instinct, and when consuming artificial sweeteners their instinct was to eat more and get fat.

While these studies demonstrate that artificial sweeteners cause weight gain by encouraging people to eat more, the question of "Why?" still remains. To answer that, let's take a quick look at the human brain on diet drinks:

"Increasing evidence suggests that artificial sweeteners do not activate the food reward pathways in the same fashion as natural sweeteners. Lack of caloric contribution generally eliminates the postingestive component. Functional magnetic imaging in normal weight men showed that glucose ingestion resulted in a prolonged signal depression in the hypothalamus. This response was not observed with sucralose ingestion." [8]

The postingestive signal depression comment means that the hypothalamus stopped telling the body to eat after real sugar was consumed. With sucralose, on the other hand, the hypothalamus went right on asking for food. So once again, the taste buds may have been fooled but the digestive tract was not.

Put it all together and it's clear that artificial sweeteners confuse the body's energy intake system, resulting in increased caloric consumption and weight gain.

Aspartame (Diet Coke)
Aspartame is made up of two amino acids called phenylalanine and aspartic acid, which stimulate release of the appetite and metabolism hormones, insulin and leptin.

The big problem with releasing insulin and leptin even though no calories are being consumed is that the body ends up consistently overproducing the two, resulting in leptin and insulin resistance. Resistance to these important hormones will diminish the feeling of being full after eating and also cause the body to burn less fat.

Studies on appetite and aspartame were evaluated long before appetite hormones were fully understood. In a study over 20 years old, it was found that artificial sweeteners produced significant changes in appetite [9,10].

One medical investigator, Dr. H. J. Roberts, concludes that aspartame has caused our obesity epidemic. He has personally demonstrated that this "guilt-free" sweetener induces serious cravings for carbohydrates, which are also a major component of weight gain.

Sucralose (Pepsi One)
Diet sodas sweetened with sucralose can be a problem for other reasons. Studies in rats show that sucralose depletes the good intestinal flora, which is vital for appetite and blood sugar control, and proper weight maintenance. As a matter of fact, sucralose has been shown to reduce the amount of good bacteria in the intestines by 50% [11].

There are two groups of beneficial bacteria that are dominant in the human gut - Bacteroidetes and Firmicutes. Studies have shown that the relative proportion of Bacteroidetes is decreased in obese people by comparison to lean people, and that this proportion increases again when weight is lost on certain types of low-calorie diets [12].

If this information on Splenda wasn't bad enough, the research also suggests that nutrient absorption maybe negatively impacted [13].

Increased Artificial Sweetener Consumption
As shown in the following chart, the consumption of artificial sweeteners has exploded in the last three decades, closely mirroring the growing obesity epidemic.



Obesity in America is a more complex issue than just artificial sweeteners, our increased consumption of refined sugar and nutrient-poor processed foods must be taken into account, but it's certainly one piece of the puzzle.

References
[1] Fowler SP, Williams K, Resendez RG, Hunt KJ, Hazuda HP, Stern MP. Fueling the obesity epidemic? Artificially sweetened beverage use and long-term weight gain. Obesity (Silver Spring, Md.) 2008;16:1894–1900.
[2] Stellman SD, Garfinkel L. Artificial sweetener use and one-year weight change among women. Prev Med. 1986;15:195–202.
[3] Black RM, Leiter LA, Anderson GH. Consuming aspartame with and without taste: differential effects on appetite and food intake of young adult males. Physiol Behav. 1993;53:459–466.
[4] Rogers PJ, Carlyle JA, Hill AJ, Blundell JE. Uncoupling sweet taste and calories: comparison of the effects of glucose and three intense sweeteners on hunger and food intake. Physiol Behav. 1988;43:547–552.
[5] Lavin JH, French SJ, Read NW. The effect of sucrose- and aspartame-sweetened drinks on energy intake, hunger and food choice of female, moderately restrained eaters. Int J Obes Relat Metab Disord. 1997;21:37–42.
[6] King NA, Appleton K, Rogers PJ, Blundell JE. Effects of sweetness and energy in drinks on food intake following exercise. Physiol Behav. 1999;66:375–379.
[7] Swithers SE, Davidson TL. A role for sweet taste: calorie predictive relations in energy regulation by rats. Behav Neurosci. 2008;122:161–173.
[8] Smeets PAM, de Graaf C, Stafleu A, van Osch MJP, van der Grond J. Functional magnetic resonance imaging of human hypothalamic responses to sweet taste and calories. Am J Clin Nutr. 2005;82:1011–1016.
[9] J Am Diet Assoc. 91(1991): 686–90
[10] Tordoff MG, Alleva AM., "Oral stimulation with aspartame increases hunger", Physiology & Behavior March 1990; 47(3):555-9
[11] http://www.mpwhi.com/gain_weight_by_going_diet.htm
[12] Nature 444: 1022–1023, 2006.
[13] J Toxicol Environ Health A. 2008;71(21):1415-29

The information presented is not intended to diagnose, treat, prevent, or cure disease. Please speak with your doctor before starting any diet, exercise, or supplement program.

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