Most people begin consuming diet products not because they love the taste or want to gain extra nutrition but because they believe doing so will help them lose weight. Those sweetened with aspartame make up a large part of the “diet” products market to this day, despite plentiful research showing they likely promote weight gain, not loss. Take the 2011 study by researchers at the University of Texas Health Science Center at San Antonio.
After following 474 diet soda drinkers for nearly 10 years, researchers found that the drinkers’ waists grew 70 percent more than the waists of non-diet soda drinkers. Further, those who drank two or more diet sodas a day had a 500 percent greater increase in waist size.1,2 A similar study published in 2015 also revealed a "striking dose-response relationship" between diet soda consumption and waist circumference.
People who never drank diet soda increased their waist circumference by an average of 0.8 inches during the nine-year observation period, while daily diet soda drinkers gained an average of nearly 3.2 inches — quadruple that of those who abstained from diet soda altogether.3
Even occasional diet soda drinkers added an average of 1.83 inches to their waistline in that time period. The link between aspartame, the most used artificial sweetener worldwide, and weight gain, obesity and other health problems is so strong that some are now calling it one of the greatest consumer frauds of all time.4
Artificial Sweeteners Disrupt Your Metabolic Response
Part of the problem with artificial sweeteners is that the sweet taste they provide (in many cases even hundreds of times sweeter-tasting than sugar) does not match up with the energy (or calories) the food provides.
Your body, however, is designed to relate the two, and a recent study by Yale University School of Medicine researchers revealed that the mismatch that occurs when consuming artificially sweetened foods and beverages leads to disruptions to metabolism.5,6 In a Yale University press release, senior author and psychiatry professor Dana Small said:7
“[T]he assumption that more calories trigger greater metabolic and brain response is wrong. Calories are only half of the equation; sweet taste perception is the other half … Our bodies evolved to efficiently use the energy sources available in nature. Our modern food environment is characterized by energy sources our bodies have never seen before.”
The study found that an artificially sweetened, lower-calorie drink that tastes sweet can trigger a greater metabolic response than a drink with a higher number of calories. Your body uses the drink’s sweetness to help determine how it should be metabolized. When sweetness matches up with the calories, your brain’s reward circuits are duly satisfied. However, when the sweet taste is not followed by the expected calories, your brain doesn’t get the same satisfying message.8
This may explain why diet foods and drinks have been linked to increased appetite and cravings, as well as an increased risk of diabetes and other metabolic diseases.9,10 When you eat something sweet, your brain releases dopamine, which activates your brain's reward center. The appetite-regulating hormone leptin is also released, which eventually informs your brain that you are "full" once a certain amount of calories have been ingested.
However, when you consume something that tastes sweet but doesn't contain any calories, your brain's pleasure pathway still gets activated by the sweet taste, but there's nothing to deactivate it, since the calories never arrive. Artificial sweeteners basically trick your body into thinking that it's going to receive sugar (calories), but when the sugar doesn't come, your body continues to signal that it needs more, which results in carb cravings.
Diet Products May Promote Weight Gain
The research continues to pour in that consuming artificially sweetened products is counterproductive if you’re looking to lose or maintain your weight.
A 2017 meta-analysis published in the Canadian Medical Journal found artificial sweeteners do not show a clear benefit for weight management and, instead, may be associated with increased body mass index (BMI) and cardiometabolic risk.11 A 2013 study likewise concluded that, like sugar-sweetened beverages, “artificially sweetened (diet) beverages are linked to obesity,” and:12
“ … [A]ccumulating evidence suggests that frequent consumers of these sugar substitutes may also be at increased risk of excessive weight gain, metabolic syndrome, Type 2 diabetes and cardiovascular disease.
This paper discusses these findings and considers the hypothesis that consuming sweet-tasting but noncaloric or reduced-calorie food and beverages interferes with learned responses that normally contribute to glucose and energy homeostasis. Because of this interference, frequent consumption of high-intensity sweeteners may have the counterintuitive effect of inducing metabolic derangements.”
If you drink more than 21 artificially sweetened beverages a week, meanwhile, your risk of overweight and obesity is nearly double that of someone who does not.13 Aspartame consumption in particular has also been linked with an increased risk of abdominal obesity, which in turn is considered an important risk factor for cardiovascular diseases such as coronary heart disease and stroke.14 But when it comes to the overall health risks of artificial sweetener consumption, weight gain is only the beginning.