‘Healthy’ Foods May Be Better for Some People Than Others


People with diabetes have long known that the same food can affect different people’s blood sugar differently. Now, for the first time, there’s scientific proof: Scientists report that a food’s effect on blood sugar depends not just on the food, but on the person eating it.

Blood glucose, commonly known as blood sugar, may be best known for its association with diabetes, but it’s important for everyone to understand. Glucose travels through your bloodstream, delivering energy to every part of your body. Every time you eat, your blood sugar jumps up. Scientists call this jump a postprandial glycemic response (PPGR).

There are two popular methods for predicting how a given food will affect a person’s PPGR: the number of carbs in a food and the glycemic index. Both strategies assume that a food creates the same PPGR response no matter how it’s eaten—or who eats it.

That assumption may be flawed, says a team of researchers from Israel’s Weizmann Institute. Their new report, published last week in the journal Cell, argues that universal guidelines may actually be encouraging people to eat foods that make their blood sugar worse.

“Ascribing a single PPGR to each food … assumes that the response is solely an intrinsic property of the food,” study co-author Eran Segal told The Atlantic. “But there are very striking differences between people's responses to identical meals.” 

Segal and his colleagues recruited 800 healthy volunteers and gave them questionnaires on their eating habits and medical histories. The volunteers provided stool samples so the researchers could check out their gut bacteria. For one week, they tracked their meals and sleep using a mobile app, while a continuous glucose monitor measured their blood sugar. Everyone ate the same breakfast, but beyond that, what they ate was completely up to them. 

Studying people’s eating habits can be tricky, especially when the data is self-reported. People tend to slack or fudge the numbers when tracking their food. That wasn’t a problem for this experiment, Segal told The Atlantic. These volunteers were motivated: “They joined because we explained that we'd be able to tell them which of the foods they normally eat spike their glucose levels. They came because they wanted to know and we said that if they didn't log properly, we wouldn't be able to tell them.”

The results were dramatic, and completely unique to each volunteer. Foods that caused PPRG spikes in one person had little to no effect on another. The data showed that what and how much you eat matters, of course, but just how it matters varies immensely.

These results weren’t limited to high-carb junk food. One middle-aged woman was working hard to stick to a healthy diet that included lots of vegetables, including tomatoes. But data from her glucose monitor showed that her blood sugar spiked each time she ate tomatoes. The good-for-you produce wasn’t good for her at all.

The researchers’ next step was to turn their results into an algorithm. They recruited a fresh round of volunteers and provided each one with two customized meal plans: one “good” and one “bad.” Half of the meal plans came from nutrition experts, and the other half were generated by the algorithm.

Sure enough, the volunteers’ PPRGs improved during the “good” week—even though each person was eating something different. Even their gut bacteria changed for the better. This was true of both the man-made meal plans and those suggested by the computer; in fact, the algorithm's customized recommendations were slightly more effective than those made by the experts.

The researchers hope their results will inspire a new approach to nutrition and weight management. Co-author Eran Elinav said in a press release that the study "really enlightened us on how inaccurate we all were about one of the most basic concepts of our existence, which is how we eat and how we integrate nutrition into our daily life."

Our scientific and cultural approaches to obesity and diabetes may just be “really conceptually wrong,” he said. Scientists and medical professionals believe “we know how to treat these conditions, and it's just that people are not listening and are eating out of control," Segal said, "but maybe people are actually compliant and in many cases we were giving them the wrong advice."

Other researchers believe it may be too early to draw such strong conclusions, and note that Elinav, Segal, and their colleagues never directly compared their results to the glycemic index.

Still, these findings are making waves. The team won’t have any trouble finding volunteers for their next experiment; the wait list currently includes more than 4000 people.

Why You Never See Fresh Olives at the Grocery Store

If given a choice, most grocery shoppers prefer fresh produce over something that's been pumped full of preservatives. Yet shoppers are almost never given that choice when it comes to olives. The small, meaty fruits can be found floating in brines, packed in cans, and stuffed with pimentos, but they're hardly ever shipped to the store straight off the tree. As the video series Reactions explains, there's a good reason for that.

In their natural state, because they contain high concentrations of a bitter-tasting compound called oleuropein, fresh olives are practically inedible. To make the food palatable, olive producers have to get rid of these nasty-tasting chemicals, either by soaking them in water, fermenting them in salt brine, or treating them with sodium hydroxide.

Because of its speed, food manufacturers prefer the sodium hydroxide method. Commonly known as lye, sodium hydroxide accelerates the chemical breakdown of oleuropein into compounds that have a less aggressive taste. While other processes can take several weeks to work, sodium hydroxide only takes one week.

Afterward, the olives are washed to remove the caustic lye, then packed with water and salt to extend their shelf life, giving them their distinct briny flavor.

For more on the chemistry of olives, check out the full video from Reactions below.

[h/t Reactions]

Chloe Effron
Why Do Sour Things Make Me Pucker?
Chloe Effron
Chloe Effron

WHY? is our attempt to answer all the questions every little kid asks. Do you have a question? Send it to

Have you ever sucked on a lemon and felt your face scrunch up? Foods that are very sour contain a lot of acid and can make you pucker—wrinkle your face, squint your eyes, and press your lips together. When things like lemons, vinegar, and unripened fruit touch your tongue, your brain gets a signal that you’re eating something sour. It could be your body's way of saying "watch out!"

Your tongue has thousands of little bumps with tiny sensors called taste buds. Taste buds let you know when something is sweet, salty, sour, bitter, or savory. (Savory is also called umami. Say: ooo-MOM-eee.) Each taste bud has dozens of taste cells that have little sprouts on them that look like hair that can only be seen with a microscope. When foods dissolved in your saliva touch them, they tell the brain about the flavor of what you are eating. When they come in contact with very sour foods, your face might pucker up because the taste is strong and acidic.

Puckering when you taste something sour is often involuntary (in-VAWL-uhn-ter-ee). That means you do it without trying. It may happen because we have an instinct not to eat things that are dangerous. Of course, not all sour foods are bad for us. But some sour foods can make us sick—spoiled milk or fruit that is not ripe, for example. Reacting with a wrinkled-up face may be our body’s way of trying to warn ourselves and others to stay away from foods that might hurt us.

For further reading, check out “Why Are Lemons Sour?” over at Wonderopolis.


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