Non-caloric sweetener drinks are not as sought after as their sugar-sweetened versions and now science tells us why
New research lead by Monell Chemical Senses Center (University City Science Center, Philadelphia) has discovered that humans have a previously unknown pathway, by which the body is capable of identifying not only the presence of sugar in foods, but also their energy value. The study found that in addition to our taste buds that can identify the sweetness of foods and drinks we consume, there is a separate sensory ability that can distinguish between the foods that deliver calories and those that do not. This renders explanation why consumers seek regular soda drinks much more than their non-caloric sweetener alternatives.
We evolved deriving sugar from fruit and honey, and our taste buds are the primary sensory system that signals the presence of glucose in table sugar, honey, high fructose corn syrup. Now the human-taste experiments done at the Monell Center reveal to us that secondary to our taste buds there is another pathway directly in our mouth that is able to differentiate between the calorie-loaded glucose and the non-calorific artificial sweetener sucralose (a form of glucose that cannot be metabolised).
Artificial sweeteners were created essentially to help people control weight to prevent obesity and diabetes type 2. They are widely used in many foods, such as pies, pastries, cakes, sauces and dressings, low-calorie foods, energy and protein bars, protein powders, etc. But the biggest use of artificial sweeteners is in the soft drinks industry. The British Soft Drinks Association lists 11 different types of sweeteners that are licensed and “safe for use” in the UK, they include: “Acesulfame-K, Advantame, Aspartame, Aspartame-acesulfame salt, Cyclamate, Neohesperidine Dihydrochalcone, Neotame, Saccharin, Steviol Glycosides, Sucralose and Thaumatin”.
The debates on the efficacy, safety and weight control benefits of zero drinks (due to their main component being artificial sweeteners) have been going on for a very long time. There are multiple type studies, including observational, retrospective, randomised double blind, together with meta analyses and scoping reviews. They all come to a somewhat repeating conclusion: there is data supporting the claim that artificial sweeteners lead to weight gain and obesity, and there is also data supporting the opposite - artificial sweeteners do not affect weight.
As this scoping review points out, most studies group artificial sweeteners into the same class, however, the mechanisms of those are so diverse, and their metabolism and impact on insulin, and hormones of hunger and satiety are different.
The main, and I should say, perhaps one of the oldest criticism towards zero drinks has been focused on the artificial sweeteners’ ability to affect our hunger and satiety cues via the changes in the hormones ghrelin and leptin. There are studies showing that unlike glucose which carries calories, artificial sweeteners dampen our satiety and do not affect ghrelin (the hormone of hunger). Missing the cue for satiety often leads to overeating (which may or may not include drinking more soda), which then sets the pattern for later weight gain.
The other big criticism of artificial sweeteners is due to their effect on human gut bacteria. There are once again studies supporting both sides of the hypothesis: the first group claiming that due to changes in the gut composition the metabolic markers are affected resulting in insulin resistance and overweight. And the other group supporting the opposite - that gut bacteria remain unchanged. However, as I was finishing writing this blog, I found it difficult to pool the data on the second hypothesis, there are more and more studies coming out showing that sweeteners indeed cause detrimental effects on gut microbiota. Read more
The study in the journal Nature quite adamantly claims artificial sweeteners show changes both in rodent and human microbiota to promote the metabolic markers associated with obesity.
A most recent study found that saccharin, sucralose, and aspartame at the concentrations easily achieved in human daily eating, increase biofilm formation, as well as the ability of bacteria "to adhere to, invade and kill mammalian gut epithelial cells". The bacteria growing in biofilms are less active in protecting the body against pathogens and are more likely to have virulence factors and exotoxins.
The research mentioned here has been published in several peer review journals: two groups of mice were given either water sweetened with a choice of aspartame, saccharin or sucralose or plain water. The amount of sweeteners included in the drinks was equivalent to four diet sodas per day for a human. After a week of experiments, the mice given sweeteners had higher blood sugar levels than mice who drank plain water. The researchers concluded that the changes in the gut bacteria in the mice given sweeteners leads to weight gain and risk of diabetes 2.
However, the biggest concern over most of studies on artificial sweeteners is that they look at several sweeteners at the same time. In addition, many of them have data on rodents, few have data on adults. Thus it becomes quite difficult to decipher as to which of the sweeteners is not harmful, mildly harmful or a big offender for humans.
The authors demonstrate that acesulfame K, saccharin, cyclamate, neotame, advantame, sucralose in recent animal and human studies showed the kind of changes in the intestinal microbiota that are related to altered metabolic pathways linked to glucose tolerance and weight gain. They highlight the detrimental changes seen in saccharin on the human gut bacteria. A class of polyols, such as erythritol, hydrogenated starch hydrolysates, isomalt, lactitol, maltitol, mannitol, sorbitol, and xylitol were part of this review with ranging results, some found helpful for the intestinal bacteria growth, some causing symptoms associated with IBS - flatulence, bloating, laxative effects.
The new research by Monell Center throws interesting light on the subject of artificial sugars. If the human mouth is able to detect calories in food and drinks separate to their sweetness factor, it is perhaps that one step needed for us to change our position on artificial sugars and their use for weight control and diabetes prevention. Whether it is via altering ghrelin secretion and hunger cues or the effects on the gut bacteria that lead to metabolic changes, the talk about which part of artificial sweeteners is harmful for health is not that important, as far as I can see. What is more important, in the words of Liz Lipsky, PhD, CNS, FACN, IFMCP, Director of Academic Development for the Nutrition programs at Maryland University of Integrative Health, our body finds it very hard to digest, absorb and utilise industrially created foods, in most cases treating them as ‘foreign’.
So why would you want to compromise your health with food-like substances researchers themselves find it difficult to reach consensus on?