BASICALLY, IT’S THAT THE STUDIES ARE POLITICIZED AND JOURNALISM STINKS: The Problems With Food and Exercise Studies.

Nearly everything you have been told about the food you eat and the exercise you do and their effects on your health should be met with a raised eyebrow.

Dozens of studies are publicized every week. But those studies hardly slake people’s thirst for answers to questions about how to eat or how much to exercise. Does exercise help you maintain your memory? What kind? Walking? Intense exercise? Does eating carbohydrates make you fat? Can you prevent breast cancer by exercising when you are young? Do vegetables protect you from heart disease?

The problem is one of signal to noise. You can’t discern the signal — a lower risk of dementia, or a longer life, or less obesity, or less cancer — because the noise, the enormous uncertainty in the measurement of such things as how much you exercise or what exactly you eat, is overwhelming. The signal is often weak, meaning if there is an effect of lifestyle it is minuscule, nothing like the link between smoking and lung cancer, for example.

And there is no gold standard of measurement, nothing that everyone agrees on and uses to measure aspects of lifestyle.

The result is a large body of studies whose conclusions are not reproducible. “We don’t know how to measure diet or exercise,” said Dr. Barnett Kramer, director of the National Cancer Institute’s division of disease prevention.

This has always been true, but it hasn’t prevented them from disseminating commandments with an air of unshakable scientific certainty.