How Sugar Can Cause Obesity and Diabetes


A recent study on mice helps us understand how eating sugar can cause diabetes and obesity (Cell, August 29, 2022). Eating excess sugar can cause loss of protective T Helper cells (TH17 cells), to allow overgrowth of harmful bacteria that damage the linings of your gut and increase absorption of calories and fat when you don’t need them. Eliminating sugar from the mice’s high-fat diet protected them from developing obesity and metabolic syndrome. Human studies have also shown that excess sugar depletes TH17 from the gut lining (Cell Metabolism, March 21, 2022), and that diabetes is associated with depletion of TH17 cells (Cell Reports, May 25, 2021;35:109176).

  • You have both healthful and harmful bacteria living in your intestines.
    • The healthful bacteria are happy with the food you eat while it is still in your intestines, so they do not try to enter your colon cells to look for additional food.
    • The harmful bacteria are not happy with the food that you eat, so they look for food inside your cells and try to enter your colon cells.
    • Your immunity tries to defend you from these invading bacteria by producing cells and chemicals that attack, and try to kill, the invading bacteria.
    • Your immunity produces T Helper cells (TH17) that line your gut and help to prevent harmful bacteria from entering your colon cells.
    • They help to prevent fat that you have eaten from being absorbed when you take in more food than your body needs, so potentially TH17 cells help to protect you from developing diabetes and obesity.
    • The number of TH17 immune cells is controlled by different types of bacteria in your colon. The more TH17 cells you have, the lower your risk of developing diabetes and high blood sugar levels. Other factors like not overeating and avoiding pro-inflammatory foods are also important.

More on Dietary Sugar and Harmful Gut Bacteria
Dietary sugar is supposed to be absorbed in the upper intestinal tract, but research from Yale suggested that taking in excessive amounts of sugar can cause some of the sugar to pass through the intestines unabsorbed. This sugar arrives in your colon where it can harm you by keeping healthful bacteria from growing in your colon and encouraging the overgrowth of harmful bacteria (PNAS, Dec 17, 2018). Unabsorbed sugar in your colon can prevent the good bacteria from producing a key protein called “Roc” (“regulator of colonization”), which is required for growth of the healthful species Bacteroides thetaiotaomicron (B. theta) in your colon. This research was done in mice, but it should also apply to humans.

Avoid Becoming Diabetic
More than 70 percent of North Americans will become diabetic. More than 30 percent of type II diabetics don’t know that they have diabetes because their fasting blood sugar is normal, at less than 100 mg/dL, so their doctors have told them that they are not diabetic. People who have fasting blood sugar levels between 100 and 125 mg/dL are often told that they have “pre-diabetes,” when they are already at very high risk for heart attacks (BMJ, 2016;355:i5953). A review of 129 studies found that tests for a high rise in blood sugar after meals were better than tests of fasting blood sugar levels as a predictor of coronary heart disease, strokes, or death from any cause (BMJ, July 17, 2020;370:m2297). Having a blood sugar greater than 155 mg/dL one hour after you eat a meal markedly increases your risk for heart attacks, strokes and premature death, even if your fasting blood sugar is normal (Atherosclerosis, Nov 17, 2016;256:15-20). This test is more dependable than HBA1c, the test used by most doctors to diagnose diabetes today (J Clin Endo & Metab, Nov 15, 2018).

My Recommendations
I believe that everyone should limit or avoid foods with added sugars and fruit juices. More than seventy percent of people with “pre-diabetes” eventually develop diabetes (Diabetes Care, 2020;43(Suppl 1):S32-6). See Lifestyle Changes to Prevent and Treat Diabetes