YMMV

YMMV. Or “Your Mileage May Vary.” That’s what many of us type 2 diabetes patients have discovered when it comes to diet. What works for one person may not work so well for another.

For example, some patients report that they can eat rice without a great effect on their blood glucose (BG), but potatoes make their BG levels soar. Others report the exact opposite.

One problem with such annecdotal reports is that we often don’t know how the various foods were cooked, how much the people ate, or what they ate with the foods they’re reporting on. For this reason, medical professionals tend to ignore such annecdotal results and instead rely on huge nutritional studies that usually report results only as averages, neglecting the “outliers,” or those whose results were far from the mean.

That means that if you’re an outlier yourself, the “evidence-based medicine” results from the nutritional studies, or the diet advice of some diet guru, may not apply to you, and if you try to follow this advice and don’t get good results, people may accuse you of being “noncompliant” or not doing what they told you to do.

But now it appears that even the professionals are beginning to accept that we’re all individuals with individual responses to various foods. And we now have a well-controlled study to support this view.

The study by researchers at the Weizmann Institute of Science in Israel used continuous glucose monitors to measure the BG levels of 800 healthy and prediabetic people after their meals for a week, and put this information along with what they ate, information from stool samples, and other physiological information into computers and analyzed it. They even gave them identical foods for some of their meals.

What they found was that the people differed greatly in how they responded to various foods; the glycemic index, a measure of how much your BG levels are supposed to rise after eating carbohydrate, varied among the participants. “In some cases, individuals have opposite response to one another, and this is really a big hole in the literature," said Eran Segal, the lead author of the study.

"After seeing this data, I think about the possibility that maybe we're really conceptually wrong in our thinking about the obesity and diabetes epidemic," he added. "The intuition of people is that we know how to treat these conditions, and it's just that people are not listening and are eating out of control--but maybe people are actually compliant but in many cases we were giving them wrong advice."

As an example, they cited the case of an obese woman who couldn’t lose weight despite trying hard. It turned out her BG levels spiked when she ate tomatoes, and because they’re supposed to be a healthy food (“eat more fruits and vegetables”), she was eating a lot of them  and her BG levels were spiking every day.

Not only glycemic index but other parameters resulted in different effects in different people. Some people saw increases in BG levels after meals that were unrelated to the carbohydrate content. In most people, fat reduced postprandial BG levels, but in some it had no effect.

What was especially interesting was that the variation in responses to food seemed to be linked with the microbiota, the bacteria in their guts. Although the microbiota tends to be stable throughout one’s lifetime, the researchers said they were able to alter the patients’ microbiota by controlling increases in the BG levels.

I think this study is important in the context of “diet wars.” Low carbers and low fatters and other diet gurus often act as if theirs is the only diet that will work and everyone should follow in their footsteps. Their diets do work extremely well for some people, but they don’t work for everybody.

If the Kitavans thrive on a high-carb diet, that’s the diet they should follow. If the Inuit thrive on a high-fat diet, that’s the diet they should follow. The diet you should follow may depend on the bacteria in your gut, and that may depend on your genetic heritage, although it can be somewhat altered in various ways (diet, antibiotics, etc.).

In the diabetes community, I think most people are aware of the concept of YMMV, and we’ve adopted a philosophy that takes it into consideration, namely “Eat to Your Meter.” If some food like tomatoes makes your BG levels soar, don’t eat that food. If it’s relatively benign for you, go ahead and eat it in moderation, and don’t worry if someone else says it’s no good for them.

For those without diabetes who simply want to lose weight, an analogous approach would be “Eat to Your Scales.” If you tend to gain weight when you eat certain foods, then don’t eat them.

Although most of us would agree that a diet of nothing but cheeseburgers and fries is not healthy for anyone, what is healthy is less certain. Remember YMMV and eat what works for you.

Parsing the Popular Press

Science, especially nutritional science, usually moves in small steps forward and then small steps steps backward and then more steps forward and a few steps sideways until we eventually arrive at the truth. One experiment or one nutritional study proves nothing. It has to be confirmed, preferably several times, in order to be accepted as true.

Unfortunately the popular press has no understanding of this. The popular press also has no understanding of statistics and what “significant” means in statistical terms. So a single study is often be blown up and spread all over the popular press. The conclusions are simplified. And if that single study confirms the average person’s preconceptions, the study will be blown up even more and simplified even more.

The obvious recent example is the study about red and processed meat and cancer.

This was a meta-analysis, and such analyses have known problems. Nutritional studies also have known problems as most of them use questionnaires, which requires people to remember how many times they ate Food X over the last week or month. I often can’t remember what I had for breakfast,  and my diet changes with the seasons and with what foods are on special that week. I haven’t the slightest idea how often I ate spinach in the last month.

Furthermore, the meat study was about only colorectal cancer (CRC). The conclusion was that “the state of the epidemiologic science on red meat consumption and CRC is best described in terms of weak associations, heterogeneity, an inability to disentangle effects from other dietary and lifestyle factors, lack of a clear dose-response effect, and weakening evidence over time.”

But the popular press ran articles with titles like “Meat as dangerous as smoking.” This is the sort of soundbite people will remember. No one will remember “weak associations” or “lack of a clear dose-response effect” even if they know what that means, or the fact that the study is limited to CRC.

Numerous diet bloggers have pointed out the limitations of this red meat study, including Zoe Harcombe and Stephan Guyenet. I don’t want to do that here, just point out how the popular press misleads the public in order to get sensational stories.

Another story that captured the attention of the popular press was a story claiming that red wine can improve cardiovascular health in people with type 2 diabetes. This is the type of story that the general public can understand, and it’s appealing to people who like to drink, so it was played large in a lot of the popular press.

These news stories are often based on just one study, and just one study proves nothing, especially if it’s a nutritional study. So the probability that further research will contradict the study the press has blown up is high. If it is, some readers (or TV watchers) decide that no health information is trustworthy and may ignore even advice based on good research that has been confirmed many times.

Here is an example of a study of chimpanzee communication claiming that their results disprove previous results by another group. And here is a study contesting the source of DNA samples supposed to be from ancient grains. They claim the results stemmed from contamination with modern grains. And here is a story refuting the idea that sitting for long periods of time is bad for your health even though you get exercise at other times.

One might conclude that no scientific studies are worth reading about because next week someone will claim the opposite. That’s not true. Often studies are confirmed by other researchers. It’s just that we have to interpret any studies as tentative, and especially if they’re funded by a group that sells the product, for example, a study by the US Gloopyberry Association showing that gloopyberries reduce cholesterol levels when you eat the equivalent of five pounds a day. The popular press would run stories with headlines like “Gloopyberries reduce cholesterol,” and people would buy more gloopyberries, which of course is why the Gloopyberry Association funded the study.

Many of the foods we eat have effects on the compounds in our blood, especially when eaten in excess, and most of them have never been tested. In fact, some of them might have a greater effect on cholesterol than the gloopyberries but we won’t know until someone studies them in reasonable amounts, and this requires funding for the study.

Derek Lowe has a blogpost about another problem with popular press articles. That is the tendency to label the results of studies as “breakthrough” or “miracle” cures when in fact they represent baby steps on the way to the solution of some problem. Most articles by science news organizations like Science Daily or Eurekalert are simply press releases from the institutions whose scientists did the experiments. Quite often you’ll see two or even three articles about the same research, each one emphasizing the researchers from their institution.

Their job is to put the best possible spin on their institutions, and “breakthrough” studies are a good way to do this. They also provide suggested headlines, which these science news sites usually use. Easier than writing their own.

The popular press then reads the Science Daily or Eurekalert stories and simplifies even more and that’s what most people read or hear on the evening news.

So what can we as intelligent readers do? We can’t ignore all these studies. But we have to file them away as “interesting and perhaps with some truth in them.” Then we can wait to see if the work is confirmed.

This isn’t as exciting as thinking that eating gloopyberries will solve all our problems and do our taxes for us. But it’s closer to reality. We can’t control the popular press. But we can control our reactions to the popular press articles. Sometimes ignore is the best solution, I think.