Ever since 1963, when the Coca-Cola Company launched Tab and Pepsi countered with Patio Diet Cola (later renamed Diet Pepsi), sugar-free, zero-calorie diet sodas have been the default option for millions of people looking to stay slim while still indulging their sweet tooth. The sugar substitutes contained in these enormously popular products – from cyclamates to saccharin to aspartame to stevia – made an irresistible offer. You can have all the sweetness of sugar with none of the guilt (or weight gain).
The year 1963 also marks the beginning of another phenomenon in America. In that year, roughly 13 percent of Americans were considered obese, which is to say they had a Body Mass Index (BMI) of 30 or higher. (For a 5-foot-ten-inch male that corresponds to a weight of 209 pounds.) Today, that number is 40 percent and rising for American adults age 20 and over, according to the US Center for Disease Control. Even adolescents aged 12 to 19 years have seen their rates of obesity skyrocket from roughly 4 percent in 1963 to 20.6 percent today.
So what happened? Where is our future paradise of slender, fit people enjoying zero-calorie drinks? Now, granted, there has always been a portion of the population that simply eats too much and gets little or no exercise. But the vast majority of us at least aspire to be thinner and more fit. We're going to the gym at least semi-regularly; we're making healthy food choices and limiting caloric intake where we can; and we're drinking a LOT of diet soda. And yet we struggle with our weight and still get heavier.
Indeed, observational studies suggest that people who regularly consume zero-calorie drinks with artificial sweeteners had a higher risk for health issues like weight gain, obesity, Type 2 diabetes and heart disease. A higher risk! For years, scientists attributed this effect to reverse causation, the notion that diet soda wasn't making people fat, but rather, overweight people (being more worried about their physical condition than thin people) were more likely to drink diet soda.
This was a comforting theory that just didn't hold water. The numbers were too stark, the growing health emergency too dire. Now scientists have begun, finally, to investigate how our bodies are reacting to the artificial sweeteners so prevalent not just in our diet sodas, but in all manner of foods we have been consuming in ever-increasing amounts since 1963. Some of the results have been surprising.
Here are 10 Reasons Diet Soda Is Not Making You Thin
Diet soda is elevating your craving for real sugar
Believe it or not, there was a time in American life when sweets were considered a special treat. If you grew up in the 1930s or 1940s or 1950s, Sunday dinner was special in that you might receive a small portion of pie or ice cream for dessert. If your grandfather was like our grandfather, he's probably still telling you about getting something exotic like an orange in his Christmas stocking. Nowadays, sweets are ubiquitous and present at every meal and between meals, all day. Diet sodas, because they're regarded as "no impact sweets," make up a significant portion of this daily intake. Our brains, bombarded by sweets all day, learn to crave them more and more, which paves the way for increased intake of real sugars, not just in obvious ways, like between-meal cookies and chips, but in overuse of condiments and sauces, and the prevalence of ever-increasing portion sizes and "free refills." The result of this is overeating and weight gain.
Diet soda may be encouraging insulin resistance over time
This is an area where the science is still evolving. In a December 2009 study published in the journal Diabetes Care, researchers found that test subjects who had consumed diet soda had significantly higher levels of glucagon-like peptide-1 (GLP-1). GLP-1 is a hormone that can help control blood sugar via different mechanisms including the stimulation of insulin production. Researchers hypothesized that changes in GLP-1 levels were from the stimulation of the sweet taste receptors. Constant insulin spikes throughout the day, very possibly, would undermine or degrade insulin response over time, which would facilitate increased body fat storage. This is an area of science to keep an eye on.
They're harming your "good" intestinal bacteria
The artificial sweeteners in diet soda have been engineered so that they are not digested in the stomach and pass directly into the gastrointestinal tract, which is the home of trillions of tiny bacteria of various strains. Scientists have been trying to calculate the impact of those sweeteners on various bacteria, and the early evidence is not good. Indeed, artificial sweeteners may enhance the populations of gut bacteria that are more efficient at pulling energy from our food and turning that energy into fat, while decreasing levels of other bacteria. More than 90 percent of the bacteria in our gut come from two subgroups, bacteroidetes and firmicutes. In studies, genetically obese mice have been found to have 50 percent fewer bacteroidetes bacteria and 50 percent more firmicutes bacteria than normal mice. The addition of firmicutes bacteria may have helped the animals extract more energy from their food, and triggered the storage of fat rather than its breakdown for energy. Research is under way to see if this process also occurs in humans, and to what extent artificial sweeteners are playing havoc with our gut bacteria.
Diet soda may lead to glucose intolerance
Fluctuations in the gutbiome, as it is called, can have serious repercussions. In a study published online in the journal Nature in 2014, researchers attempted to identify the bacteria that were over- or underrepresented in mice with impaired glucose tolerance, and to identify what those bacteria are doing. In the microbial ecosystems from mice that ate artificial sweeteners, the pathways that were overrepresented included several that had previously been linked to diabetes and glucose intolerance. Glycan degradation, for example, occurs when microbes digest certain chains of sugars and create short-chain fatty acids that the body can use for energy, providing extra calories. The investigators confirmed that the sweetener-fed mice had increased amounts of this end product, the short chain fatty acids, in their guts. Glucose intoleranace, of course, is a metabolic syndrome directly linked to weight gain and type 2 diabetes.
The more you drink, the more you want
This is why, for instance, the president of the United States has a red button on his oval office desk that functions solely as a "Diet Coke button." He is said to drink 12 Diet Cokes a day. The caffeine and aspartame in diet soda trigger the release of dopamine and glutamate in the brain, two neurotransmitters in the brain's reward center, that keep you hitting that red button again and again throughout the day.
Diet soda is causing mood swings
All of those blood sugar spikes and crashes have an entirely predictable effect on your mood and ability to concentrate. They're fluctuating wildly all over the place. What do you do when you experience abrupt mood swings and crashes? Often, you eat.
Diet soda is dehydrating you
Diet sodas are unusual in that they're a liquid that actually dehydrates you. The caffeine in diet soda acts as a diuretic, flushing water out of the body without replacing it. Dehydration causes all sorts of havoc at the cellular level, slowing down many of the processes – cellular recovery and repair foremost among them – that facilitate positive outcomes like muscle mass gain and fat loss.
Diet soda is decreasing your bone density
The phosphoric acid in diet soda can facilitate enhanced calcium excretion from the bloodstream, which causes the body to compensate by leaching calcium from your bones, leading to brittle, thinner bones (or osteoporosis). This process will have a direct negative impact on your workout capacity, especially as you grow older, and lead to fat gain. As an added bonus, phosphoric acid also disrupts your body's nutrient absorption process, preventing your skin and muscles from getting the nutrients they need, leading to aging and withering of your skin and muscles.
Diet soda may be putting you at risk for hypertension
Diet soda drinkers are more likely to have high blood pressure than those who don't drink diet sodas regularly. Why? Well, simply being overweight can contribute to high blood pressure. Also, a 12-ounce serving of diet soda contains 57 mg of sodium, which is 4 percent of the daily 1,500-milligram limit recommended by the American Heart Association. Those cans of diet soda can really add up.
Oh, and your liver produces carcinogens when you drink diet soda
While this effect of diet soda consumption isn't strictly related to weight gain, it's terrifying anyway. When you consume a diet soda that contains the popular artificial sweetener aspartame, your body struggles to process it. These digestive processes create a by-product called methanol, which is a toxin. Confronted with this toxin, your liver converts methanol in large part to formaldehyde, which is actually less deadly, but still, as you might imagine, a carcinogen.
Ingestion of diet soda before a glucose load augments glucagon-like peptide-1 secretion. Brown RJ1, Walter M, Rother KI. Diabetes Care. 2009 Dec;32(12):2184-6. doi: 10.2337/dc09-1185. Epub 2009 Oct 6.
Artificial sweeteners induce glucose intolerance by altering the gut microbiota. Jotham Suez, Tal Korem, David Zeevi, Gili Zilberman-Schapira, Christoph A. Thaiss, Ori Maza, David Israeli, Niv Zmora, et. Al. Nature, Vol. 514, Oct. 14, 2014.
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