What they found was that totally different foods made their glucose spike (and not the foods that the glycemic index predicted). It turned out this doctor could eat ice cream and regular soda without it affecting her blood glucose at all. (When blood glucose is too high, the glucose gets stored as fat). The Israeli researchers postulate that this partly has to do with her community of gut microbes which, as it happened, was not very diverse. But what?
Two years ago I went on the Blood Type diet for two weeks which meant I changed basically everything I regularly ate. I gave up: oranges, bananas, chiles, tomatoes, potatoes, and red meat -- and replaced them with grapefruit, pineapple, broccoli, bread, and most days I didn't eat meat at all although I could have chicken or fish up to 4x's a week. I had been feeling very healthy before I started the diet, but I felt GREAT for the two weeks I went on it. It even meant I could drink red wine and coffee, whereas I'd been living without caffeine and alcohol. So, in other words, I completely changed my diet and felt improved. But was it really the specific foods I ate/didn't eat? I began to have my doubts after a few months, and eventually returned to eating many of the foods I'd been avoiding.
I'm a sixty-year-old woman, and I don't think I have a single female friend who isn't on some sort of diet, or avoiding certain foods, or doing a cleanse, or participating in a diet program like Weight Watchers. And I'm not being critical -- I've been doing diet experiments for the last six years. And I'd say I've been successful at finding what works for me: Everything!
MyPlate, no gluten, no dairy, vegetarianism, no sugar, paleo, Wellness Cleanse, Blood Type Diet -- with each of these, I've lost some inches, lost my cravings, had increased energy, good sleep, daily bowel movements, etc. Then, just when I think I've found the perfect way to eat and get used to preparing meals in certain ways, I develop cravings again and my clothes get tight or my joints begin to ache, and I decide to try some new set of food rules.
I must point out that no matter which diet I've tried, I've stuck to whole foods. I don't eat things that come in a box, bag, or can. Very occasionally I have a bag of potato chips. And sometimes I eat at a restaurant that may use processed foods, and I do eat at friends' houses who may serve something packaged. But if I'm cooking, and I usually am, it's whole foods all the way: vegetables, seeds, nuts, fruit, grains, beans, eggs, some meat, fish, and a little dairy. I had my gut microbiota analyzed in October by uBiome and it compared most directly with that of the vegans in their database. It also said my gut microbiota was in the 88th percentile for diversity. Sounds healthy, right? I think it is, basically, so why would I ever get a big belly or have cravings?
I think the answer is lack of diversity! Let's consider again what the emergency room doctor was doing. She was following a diet -- like so many of us do -- that she thought was healthy, but her gut microbial diversity was very low. My theory is she could eat ice cream and soda without it upsetting her blood glucose because it's not just our own digestive systems that convert and deliver energy to our bodies, specific microbes help make different foods available to the blood stream and perhaps the doctor had been successful, through her diet, in starving her ice-cream-and-soda-loving bacteria to a very small number.
Remember, I'm not a doctor or a scientist. I have a degree in English, not biology, so take my theory with a big grain of salt. But my guess is, when we eat the same foods regularly, day in, day out, the populations of microbes in our guts that correspond to those foods increase to the point that they "help us" digest those foods with increasing rapidity, sending the energy from the food into our bloodstreams too fast for our bodies to use, and therefore it gets converted to fat.
Furthermore, I think that as our microbial populations grow out of control, they send us chemical signals that make us crave the foods they want. I don't know about you, but when I eat a lot of bread, I crave more bread. When I eat a lot of sweets, I crave more sweets. But if I totally give up bread or sweets, after a few days I stop craving them. I think it's because I've knocked the bread-loving or sweets-loving microbial populations back to a reasonable level. They're still in there, but at reduced numbers.
When we continuously change the foods we eat, our microbiome is more challenged, and so, I believe, it takes longer for our food to be broken down. Hence, the energy from the food becomes available more slowly. So a sensible eating strategy may be to constantly eat different foods (whole foods, of course) in order to stay satiated longer and for our community of gut microbes to stay as diverse as possible. When I think of my own behavior, and that of my women friends, we all get into ruts with the foods we prepare and eat, particularly if we live alone. And everyone complains about the foods they're "addicted to." So I'm now going to try and change that by not restricting a single thing (except commercially processed foods) from my diet -- not wheat, or dairy, or red meat, or nightshade plants, or occasional sugar-laden sweets. Half of everything I eat will still be vegetables, but otherwise no rules except VARIETY. I'll let you know how it goes.
Below are a few articles about microbes and appetite. I'll be adding more as I find them.
Diet Study Overturns All We Know About Healthy Eating, Israel21c
Why Do People Put On Differing Amounts of Weight, The BBC
Why French Fries May Be Better For You Than Salad, fromthegrapevine.com
Your Gut Bacteria May Be Controlling Your Appetite, The Smithsonian
How Gut Bacteria Make us Thin or Fat, Scientific American
Your Gut Bacteria Want You to Eat a Cupcake, The Atlantic
Do Gut Bacteria Rule Our Minds? UCSF
Low Fiber Diets Cause Waves of Extinction In The Gut, The Atlantic