Sitting Still, Your Body Can Handle Only 40 to 50 Grams of Carbs in Two Hours
Lyon estimates the average American eats 300 grams a day, "essentially three glucose tolerance tests a day."
unPAUSED with Dr. Mary Claire Haver · Muscle is the Organ for Longevity with Dr. Gabrielle LyonSit still after a big lunch and your body has a math problem. According to Dr. Gabrielle Lyon, a physician who studies muscle health, a sedentary person can safely clear only 40 to 50 grams of carbohydrate in about two hours without sending blood sugar and insulin out of range.
The reason is muscle. Lyon describes skeletal muscle as the body's largest metabolic sink, the main place where the carbohydrates you eat have to go. It is the main place where sugar from food is cleared from the blood into tissue, and a key place where fatty acids are burned. Movement decides how much it can take.
At a slow walk, Lyon says, muscle might use about 30 grams of carbohydrate an hour. Push the heart rate higher and that rises toward 70 grams an hour. By her calculation, at rest, without that muscular help, the two hour capacity tops out at that 40 to 50 gram threshold. Lyon says anything more has to be earned through training or it pushes toward insulin resistance.
That ceiling is easy to hit. Government guidance sets the recommended daily carbohydrate intake at about 130 grams, but Lyon estimates average American intake at about 300 grams a day. A standard diabetes check, called an oral glucose tolerance test, gives a person 75 grams of glucose and watches what happens over two hours. Eating 300 grams is, in her phrase, essentially taking three of those tests every day.
Lyon says that since roughly 75% of people do not meet basic activity recommendations, many people are eating the equivalent of repeated glucose tests each day without the muscle activity to handle it.
Lyon said she reached that conclusion after seeing a lean woman in her New York City practice who had normal body fat but high blood sugar and insulin. The woman looked thin and her body fat measured normal, in the 20s to low 30s, yet her blood sugar was high, her insulin was high, and her triglycerides were out of balance. An InBody scan, which measures body composition through bioimpedance, showed very low muscle, close to sarcopenic. It was not a body fat problem, Lyon concluded, but a muscle problem, with signs of type 2 diabetes without extra weight.
The takeaway is practical. If a meal is far from exercise, Lyon says, keep the carbohydrate portion near what idle muscle can handle. If you want more, move first and let the muscle do its real job.
Questions people ask
What does 40 to 50 grams of carbohydrates look like in food?
It is much smaller than a restaurant meal. It is roughly a medium bagel, about two slices of bread plus a banana, or about one 12-ounce regular soda. A burrito bowl with rice, beans, and a tortilla can easily hold two to three times that amount in one sitting.
Does walking after a meal actually help?
That is Lyon's logic. Contraction lets muscle pull in glucose and burn more carbohydrate, rising from about 30 grams an hour during slow walking toward higher rates as effort rises. Without that activity, the carbohydrate still 'has to go somewhere,' as Lyon puts it, and muscle is the main place for it to go.
Can you raise your carbohydrate tolerance?
You can raise the muscle side of the equation, though mostly through activity rather than diet alone. More muscle mass and regular resistance training plus aerobic movement increase glucose disposal and fatty acid burning. Better sleep and gradual weight loss can also improve insulin sensitivity.