A study from Israel found that two artificial sweeteners, saccharin and sucralose, significantly raised blood sugar levels in healthy adults. Transferring their colon bacteria to mice caused the mice to suffer the same elevations in blood sugar (Cell, August 19, 2022).  Artificial sweeteners can harm you by altering the bacteria in your colon (Nutrition Today, May 6, 2021;56(3):105-113).

Some artificial sweeteners may cause inflammation, a condition in which your own immune system, which is supposed to kill invading germs, stays active all the time to attack you (Int J Mol Sci, May 15, 2021;22(10):5228).  These authors found that just two cans of diet drinks that contain the most widely used artificial sweeteners (saccharin, sucralose, and aspartame) increased growth and colon invasion of Enterococcus faecalis (harmful colon bacteria that invade the colon cells to turn on your immune system), and decrease the healthful E. Coli bacteria that do not invade your colon cells.

You have more than 100 trillion bacteria in your colon. Some are healthful, while others can harm you. The types of bacteria in your colon are determined far more by what you eat than by your genetics (Nature, 2018;555(7695):210-215), and some types of bacteria can turn on your immune system to cause inflammation that increases risk for heart attacks, dementia, auto-immune diseases and certain cancers (J Alzheimers Dis, 2017;58:1-15).

Colon bacteria eat the same foods that you do. The healthful bacteria are content to eat what you eat, so they stay in your colon and do not try to cross into your cells and bloodstream, but the harmful bacteria seek different foods by invading the cells lining your colon. Your immune system tries to defend you by producing huge amounts of white blood cells and chemicals that work to destroy the invading bacteria by punching holes in their outer membranes and trying to kill them. This constant invasion of your colon cells by harmful bacteria can cause your immune system to stay on all the time and attack you in the same way that it kills germs. See Prebiotics and Probiotics

Approved Artificial Sweeteners 
Artificial sweeteners are components of food that cause a sweet taste in your mouth without causing the gain in calories that you get when you eat sugars. They do this by being so sweet that you can get the taste of sugar by using only a very small amount. Non-nutritive sweeteners that have been approved by the U.S. Food and Drug Administration (FDA) are:
• Aspartame (Equal® or NutraSweet®)
• Acesulfame potassium (Sunett® and Sweet One®)
• Neotame
• Saccharin (Sweet ‘N Low, Sweet Twin and Sugar Twin)
• Sucralose (Splenda, Equal)
• Stevia (Truvia, Stevia in the Raw, SweetLeaf, Sweet Drops, Sun Crystals, PureVia)
• Monk fruit extract (Monk Fruit in the Raw)
• Advantame

As far as I know, only saccharin, sucralose and stevia have been shown specifically to change the composition of the gut microbiome, but others may have the same effect.

Artificial Sweeteners Can Increase Risk for Weight Gain and Diabetes
Many studies show that artificial sweeteners make you hungry so that you eat more food, increasing your risk for weight gain and diabetes. A review of 30 studies showed that artificial sweeteners are associated with weight gain, increased waist circumference, and higher incidence of obesity, hypertension, metabolic syndrome, type II diabetes and heart attacks (Can Med Assoc J, Jul 17, 2017;189(28):E929-E939).

Sugar is Worse Than Artificial Sweeteners
Sugared drinks are arguably the most health-harmful components in the North American diet. The Nurses’ Health Study and The Health Professional’s Follow-Up Study, two of the largest studies with data on the subject, showed that sugar-sweetened beverages are associated with increased risk for heart attacks, diabetes, obesity, strokes, high blood pressure and premature death, and the more sugar-sweetened beverages you take in, the more likely you are to suffer from these diseases (Circulation, April 30, 2019;139:2113–2125). More than 50 percent of North American adults drink at least one sugared beverage each day.

My Recommendations
• Restrict or avoid foods and drinks with added sugar. Most of the medical community now agree that sugar added to foods and drinks can increase your risk for weight gain, heart attacks and certain cancers.
• Artificial sweeteners appear to be safer than sugared foods and drinks, but increasing numbers of scientific papers show that artificial sweeteners can change the bacteria in your colon to increase risk for gaining weight and developing diabetes.
• If you are overweight and want to lose weight, I recommend adopting an anti-inflammatory diet that restricts sugar-added foods and drinks, mammal meat, processed meats, fried foods and refined grains (foods made from flour). Also try to exercise every day.
Drink Water Instead of Sweetened Drinks
Artificial Sweeteners Are Not Benign