Diets: One size does not fit all

Overeating season kicks off this week as we stock our refrigerators and wonder how to fit pies, corn casseroles, and a turkey on the same shelf. Not to mention the same grumbling stomach.

By the new year, resolutions have many struggling to pay the price of indulgence. Ever wonder why your best friend’s diet doesn’t seem to work for you? Or — as we middle-aged women inevitably notice — why men seem to eat the same things in twice the amount without gaining (as much)?

Turns out, came the news last week, science can answer both. Back in 2014, University of Texas researchers found the microbes living in the guts of males and females react differently to diet, even when the diets are identical. One suggested explanation was hormones.

But the lines aren’t simply drawn by gender. When it comes to diets, one size doesn’t fit all.

A new study published Nov. 19 in the journal “Cell” found different bodies, even among same gender and age groups, respond differently to the same meal.

Scientists at the Weizmann Institute in Israel focused on the glycemic index (GI), which measures how food affects blood sugar, in 800 adults aged 18 to 70. Some were pre-diabetic. What they learned is that, contrary to prior understanding, the GI is not a fixed number. It varies by individual. This is big news in the dieting world; it means what’s “healthy” for me may not be for you, and vice versa.

Analyzing the impacts of 46,898 meals, and taking into account lifestyles and overall health, the researchers easily confirmed that body mass index impacts blood glucose. This, we knew; the more overweight we are, the harder it is to digest and lose weight. However, they also noticed that different individuals had vastly different responses — sometimes opposite responses — to the same food, although their own reactions to food did not vary day to day.

What does this mean? For a diet to work, it should be tailored to the individual’s biology, the researchers concluded. While some things are universally true (excesses of sugar and fat are bad), other things vary. For example, a body’s responses to certain kinds of carbohydrates, or as one woman was surprised to learn, tomatoes, may cause spikes in that individual’s blood sugar when it doesn’t in others.

To further test findings the researchers designed two sets of week-long, experimental diets, one personalized “good diet” and one non-personalized “bad diet.” Results confirmed their initial conclusions: The good diets worked, the non-personalized bad diets, not so much (or not at all). They also found that those microbes important for digestion shifted in a positive way; while the personalized diets themselves varied, the microbe situation improved in the same way in each individual while on the “good” diets.

This implies, wrote the authors, that we have been “really conceptually wrong” in our thinking about dieting, obesity, and diabetes. For more information, see Cell.com/cell/current.

Sholeh Patrick, J.D. is a columnist for the Hagadone News Network – Sholeh@cdapress.com.