What You Should Be Drinking if You Need to Lose Weight

Dr. Frank Shallenberger, MD

May 30, 2023


Weight gain in many people is a vicious cycle. The fatter they are, the more insulin resistance they have. And as their insulin resistance increases, their bodies compensate by making more insulin.

But insulin blocks fat metabolism. So for people stuck in this cycle, the only way they are going to be successful at losing weight is to decrease their insulin levels.

The easiest way to do that is to exercise and cut out carbohydrates. But there is another way.

Researchers were studying a marker in the blood called C-peptide. C-peptide is formed in the body in direct proportion to how much insulin the body makes. The higher the C-peptide, the more insulin the body is making. So the researchers measured the C-peptide levels in a group of 2,112 healthy women from the Nurses’ Health Study. Some of them were obese. Some were thin. And some were in between.

Then they looked at the amount of coffee and/or caffeine each woman was taking. What they discovered was striking.

In all of the women, the more caffeine they took, the lower their C-peptide levels were. For those who drank more than four cups of coffee a day, the C-peptide levels were 16% less. Now I know that 16% doesn’t sound like much. But in terms of C-peptide levels, it’s very significant.

However, the results were even better with the overweight women.

The decrease in C-peptide was 20% lower in the women who were overweight. And there was a whopping 27% decrease in the obese women. Interestingly, they did not find the same effect from tea, although they did see an effect from decaffeinated coffee. Why?

Although tea has some caffeine, it doesn’t contain much. And decaf coffee really isn’t decaf. It has anywhere from 8.6 to 13.9 mg of caffeine per cup. But it is obvious that there must be something else in coffee other than caffeine that decreases C-peptide levels.

The authors summed it up this way, “Our findings suggest a potential reduction of insulin secretion by coffee in women. This reduction may be related to other components in coffee rather than caffeine.”

So if you’re a woman having trouble with weight control, you might be stuck in the elevated insulin vicious cycle. You can break that cycle by doing three very simple things.

• Exercise for 30 minutes every day.

• Cut carbohydrates (fruit, starchy foods, flour, sweets) from your diet.

• Take two to four cups of coffee per day. This should be an especially effective remedy for you if your doctor tells you that your insulin levels are over 10.

By the way, although this study just looked at women, I am sure the results would be similar for men.


Wu, T., W.W. Willett, S.E. Hankinson, et al. “Caffeinated coffee, decaffeinated coffee, and caffeine in relation to plasma C-peptide levels, a marker of insulin secretion, in U.S. women.” Diabetes Care. 2005 June;28(6):1390-6.

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