Chapter 20
A Boost from Beans
In 1980, it was already known for certain that beans trigger an “extraordinarily” low blood sugar response, about half as much as other common foods. But two years later, a sensational discovery was published: legumes can have beneficial effects on metabolism even hours after being eaten—indeed, even the next day. If you eat lentils in the evening, your body reacts differently to breakfast eleven hours later. Even if you drink sugar water the next morning, your body handles it better. At first, researchers called it the “lentil effect,” but when later studies found that chickpeas work too, they changed the name to the “second-meal effect.”
How does it work? We do something for our gut bacteria, and they do something for us. The gut flora takes the fiber we eat and makes short-chain fatty acids for us, which are absorbed into the bloodstream and circulate through the body. So if we eat a bean burrito in the evening, the gut bacteria eat that same burrito in the morning, and the by-products generated in the process affect how we digest breakfast. That partly explains why diabetics randomized to eat a cup of beans, chickpeas, or lentils every day had better blood sugar control.
Why Not a Low-Carb Diet?
Contrary to popular belief, a piece of fruit with a meal reduces the blood sugar response rather than increasing it, which is why people with type 2 diabetes are no longer advised to restrict their fruit intake. In half a dozen randomized controlled trials, foods—for example, carbohydrates with a higher glycemic index—were swapped out for fruit, and on average blood sugar improved significantly. The fact is, those who eat a ketogenic diet and avoid fruit in order to lower blood sugar make everything worse in the long run.
On a ketogenic diet, you may quadruple your intake of saturated fat, and saturated fat impairs the action of the blood-sugar-lowering hormone insulin. For almost 100 years, we have known that a high-fat diet can double the blood sugar response to the same carbohydrate intake within days. A single meal can do it. If you eat, for example, 100 grams of butter or drink a milkshake, insulin resistance can increase dramatically within hours. But what if people following a keto diet stick to the program and avoid carbohydrates to remain in a state of ketosis? Then AGE levels can shoot up.
One reason diabetics suffer from nerve and arterial damage is methylglyoxal, an inflammation-promoting metabolic toxin that forms when blood sugar is high. Methylglyoxal produces by far the most AGEs.
Because AGEs are concentrated in fatty and protein-rich animal foods, on a keto diet you have to expect exposure to a large amount of preexisting AGEs. At the same time, it follows that because of presumably low methylglyoxal levels in the setting of low blood sugar levels, one would expect less internal, new AGE formation. Astonishingly, researchers from Dartmouth found more methylglyoxal. After only two or three weeks on the Atkins diet, participants recorded a significant rise in methylglyoxal levels, and those who were in active ketosis fared even worse, experiencing a doubling of the glycating toxin in the bloodstream.
High sugar levels may not be the only way to generate methylglyoxal. One of the ketones produced on the ketogenic diet is acetone. Does that sound familiar? It is a main ingredient in nail polish remover. But acetone can do more than dissolve paint, give keto devotees “rotten-apple breath,” and make them fail a breathalyzer test. In the blood it can be oxidized to acetol, which may be a precursor of methylglyoxal. That may be why nondiabetics on a keto diet can have methylglyoxal levels as high as people with untreated diabetes.
What about natural and artificial sweeteners?
When participants were randomized to receive beverages sweetened with aspartame, monk fruit, or stevia instead of 16 spoonfuls of sugar (the amount in a half-liter bottle of cola), they were found to do equally badly across the day with respect to calorie intake, blood sugar, or insulin spikes. The same thing happened with the sweetener in Splenda (sucralose). How is that possible? In my video see.nf/sweeteners, I solve the mystery.
How to Dampen the Glycemic Impact of Grains
In my chapter “Blocking Calories” in How Not to Diet, I explore how the same foods can have different effects in different forms. Steel-cut oats have a relatively low glycemic index, averaging 55, whereas the glycemic index of instant oatmeal is 79, making it a high-glycemic-index food. Instant oatmeal, however, is not as bad as some breakfast cereals, which can reach an index of over 80 or over 90—even unsweetened cereals like wheat flakes. How is that possible? Breakfast cereals are industrially made using methods such as puffing or extrusion cooking, which speeds the digestion and absorption of starch, leading to extreme blood sugar responses. Wheat flakes and spaghetti are made from the same ingredient—pure wheat—but wheat flakes have twice the glycemic index.
From the standpoint of the glycemic index, breads are preferable that are made from sprouted grain with added cracked wheat, whole wheat or rye kernels, or stone-ground flour. If you can’t live without white bread, toast it, use sourdough if you bake it yourself, or freeze it and thaw it again. All of that lowers the blood sugar response.
When starch is cooked and then cooled, some of it crystallizes into “resistant” starch—starch that is resistant to being broken down into sugar by enzymes in the digestive tract, which lowers the glycemic effect. That is why pasta salad is healthier than hot pasta and potato salad is better than a baked potato. Some grains—especially sorghum and millet—naturally contain resistant starch and therefore, compared with other grains such as rice, wheat, or corn, provoke a 20 to 25 percent lower blood sugar response.
Potatoes—Defused
Most unprocessed plant foods—legumes, nuts, vegetables, and fruit—are associated with a long life. If you eat a lot of them, you have about a 25 percent lower likelihood of dying prematurely from all causes combined. Potatoes do not seem to offer that protection. Now, potatoes are not meat, which actively shortens your life, but eating them has its price, because every bite of potato is a missed opportunity to put something even healthier in your mouth that could actively lengthen your life.
The reason potatoes are only neutral with respect to mortality risk is that the harmful effect of their high glycemic index is balanced out by their fiber, vitamin C, and potassium. Can we have it both ways and eat potatoes by somehow lowering their glycemic index? There’s a cool trick: crystallization. So if we eat potatoes, for example, cold as potato salad, it’s possible to achieve about a 40 percent lower glycemic impact. To minimize the glycemic index of potatoes, boil them and eat them either cold or reheated in the microwave. The vinegar in potato salad might even add further benefit.
Sour Is Healthy
Randomized controlled trials in diabetic and nondiabetic participants suggest that blood sugar can be better regulated by adding two teaspoons of vinegar to a meal, thereby blunting the post-meal blood sugar spike by about 20 percent. So you can temper the consequences of these high-glycemic foods by, for example, adding vinegar to rice (as the Japanese do with sushi) or dipping bread in balsamic vinegar. With potato salad, it was found that cooling and vinegar add up in their effects. See see.nf/lemony to learn how lemon juice compares.
It’s the Seasoning That Matters
If you want to stick to low-glycemic-index foods, eat what grows, not what is man-made. I provide an overview of glycemic load per serving elsewhere in the book. For high-glycemic foods, vinegar is not the only way to blunt the rise in blood sugar. If you eat berries with your meals, for example, they act as starch blockers because they inhibit the enzyme that digests starch. That then slows the absorption of blood sugar in the body. So if you prepare a high-glycemic-index breakfast, add blueberries to your pancakes, or sprinkle your artificially flavored cereals with real berries.