So, there’s this thing called the glycemic index that was developed at some point as a tool for diabetics. If you’re diabetic (either Type I, where your pancreas makes no insulin at all, or Type II, where your pancreas pumps it out but your body has a lot of trouble using it properly) you’re supposed to try to keep your blood sugar levels even as much as possible. You don’t want your blood sugar to get too low: low blood sugar can kill you dead very quickly. You don’t want your blood sugar to get too high: high blood sugar can destroy your kidneys and eyes, mess up your nerve endings to cause constant pain, and wreak all sorts of other havoc. (In Type I diabetics, high blood sugar can also put you in a diabetic coma and kill you, but this is actually a lot rarer than death from low blood sugar, which is why your friends with Type I diabetes find movies that hinge on the “OH NOES! DIABETIC DOESN’T HAVE HIS INSULIN!” plot device so goddamn irritating.)
The glycemic index tries to quantify how quickly various foods will make your blood sugar shoot up. Glucose is a high glycemic-index food; kidney beans are a low-glycemic index food; most things fall somewhere between those two extremes.
There have been studies over the years that suggest that eating a lot of high-glycemic-index foods is bad for more than just diabetics. In one study, rats fed a high-glycemic-index diet gained a lot more weight, and their pancreases acted irritated and less effective. In humans, a low-glycemic-index diet has been found to be linked to a lower risk of developing Type II diabetes. Although it’s worth noting that a low-glycemic index diet is going to have lots of fruits and vegetables, beans, nuts, whole grains, and other foods generally regarded as healthy. And, in fact, a 2014 study found no real effect of paying attention to the glycemic index at all:
Study volunteers followed carefully planned diets high or low in carbohydrates and with high or low glycemic index scores. Tests tracked the volunteers’ blood pressure, cholesterol levels and sensitivity to insulin at the beginning and end of each diet. The results showed little difference between high and low glycemic index foods.
And here we come to the exciting new study that came out a couple of weeks ago.
Israeli researchers recruited 800 volunteers (some healthy, some pre-diabetic) and set them up with a continuous blood glucose monitor, and a smartphone app. They used the app to enter everything they ate throughout the day, and the data from the blood glucose monitor and the app were synchronized so that the researchers could get a very clear picture on exactly what foods caused each individual person’s blood sugar to shoot up, or not. Also, everyone ate a standardized daily breakfast.
One thing I found quite interesting to note: volunteers were not paid. They were compensated, instead, with the data gathered about their bodies, diets, and blood sugar levels, which researchers found provided their volunteers with tremendous motivation to comply with the study and enter what they were eating.
Anyway, what they found is that different people metabolize many foods differently. For instance, one woman’s blood sugar would skyrocket every time she ate tomatoes. (Tomatoes are supposed to be a low-glycemic-index food; you can find them on lists of delicious low-glycemic-index foods that you ought to be eating, in fact.)
In the second part of the study, they gave a subset of volunteers a set of specialized meals that were theoretically either a “good” or a “bad” diet for that individual. Not only did the people on the good diets see their blood sugar levels decrease, they also found alterations in their gut microbiota. The precise role of gut bacteria is not really understood at this point, which is why articles about this almost always quote scientists telling people not to experiment on themselves with probiotics because we don’t know if they’re going to make things better or worse.
…it would be foolish to run out and buy prebiotics or probiotics in hopes of losing weight or improving blood sugar, according to George Weinstock, Ph.D., who co-leads the pre-diabetes section of the Human Microbiome Project at the National Institutes of Health and who was not involved in the study.
However, in general the gut bacteria that started to flourish in the new lower-blood-sugar environment were also gut bacteria linked to better health outcomes.
“Right, that’s terrific,” my husband said when I explained all of this to him (he’s the one who pointed the initial article out to me.) “So how do I find out which foods I’m supposed to eat and which foods I’m supposed to avoid?”
Yeah, so, that’s the thing. These researchers hooked everyone up with a continuous blood-glucose monitor. Those are only barely hitting the mainstream for actual insulin-dependent diabetics, and they cost a whole lot of money.
That said, the basic finding here — that the glycemic index is only the roughest possible guideline and that foods will have an effect on you that may or may not have anything to do with the numbers on the chart — that is not news to any of my diabetic friends, most of whom check their blood sugar many times throughout the day with fingersticks and a blood-glucose monitor. So in fact, you can run this experiment on yourself, kinda, the same way a newly-diagnosed Type II diabetic does, by using a blood glucose monitor to check your blood sugar levels after meals.
The thing is, I can’t actually find much in the way of useful online instructions. When people are diagnosed with diabetes, they are supposed to be referred to a diabetes educator and given some one-on-one instructions. I am not sure how long after you eat you’d want to test your blood sugar, or how you’d narrow down the effect of individual foods. From talking to my diabetic friends, this is something that tends to require a lot of trial and error.
This is a genuinely interesting study in a lot of ways, though. First, just because of the very concrete illustration of how different foods act differently in different bodies, which is one of those things that really should be obvious and yet you’ll hear (from doctors, even) that weight is just “calories in, calories out” and no one should be worrying about anything else. (One of the more irritating articles about this study quoted the president of healthcare and education at the American Diabetes Association as saying, “What really prevents people from developing type 2 diabetes, particularly those who are at risk, is weight reduction,” like in his head it’s apparently just that simple.)
But also, it demonstrated that you can get really excellent compliance from your research subjects if you’re offering them information. It is surprisingly how rarely studies offer information to their participants. I participated in a study years ago that involved either vaccinating me, or giving me a placebo; the goal was to see whether my newborn got anything out of the vaccination. Either way, I was the one vaccinated and so for my own health records, I did want to know which I’d gotten. I was in the very last round of participants; after that, there was an analysis stage. Eight years later I finally got a letter saying that yes, I’d gotten the actual vaccine. (Also, no, vaccinating me didn’t provide my newborn with any benefits. Not every study produces exciting results.)
The researchers are now doing a follow-up study (for which they’ve been inundated with volunteers). If it turns out that this sort of thing provides really useful individual data, we may see a variant of this start to be offered as a routine procedure for people with pre-diabetic blood sugar readings. (Much like people with heart problems are sometimes put on a portable monitor for a period of time.) In the short term, though, this doesn’t really give people worried about Type II diabetes a whole lot in the way of action items.