For most of us, even when blood sugar skyrockets after a big meal, our bodies can bring it back to normal in a few hours with no problem. Only people with untreated diabetes have blood sugar levels that stay quite high most of the time.
Logically, for a long time, doctors thought that only those people needed to be concerned about the effect of food on blood sugar.
Now we know that even in healthy people, high blood sugar after meals can, over time, damage the body, even if it never causes diabetes. In short, it’s no longer just certain people who need to worry about their blood sugar; it’s pretty much everyone. It should concern you even if you’re thin and healthy, and especially if you don’t get much exercise (does that describe you? It describes most people) or you carry extra weight around your middle.
By now you’re wondering, “How can I get off the rollercoaster?” Take heart: It’s not that difficult — and we’ll show you how. Later, we’ll get into much more detail about how our diets contribute to unstable blood sugar (hint: foods like white bread, white rice, potatoes, and sugary drinks are major culprits) and which foods can help solve the problem. But for now, let’s take a deeper look at why you should care.
When you eat a big meal, especially one with a lot of starchy or sugary foods, the food makes its way through your stomach and intestines and then is converted into glucose, the main fuel for your muscles and even your brain. Voilô, instant energy!
But a big starchy meal can give the body more glucose than it needs. In fact, it can raise blood sugar levels twice as much as another, healthier meal would.
Most people’s bodies can bring blood sugar down fairly quickly, within an hour or two of eating. The body does this by releasing insulin, a hormone produced by beta cells in the pancreas. Insulin signals the body to let that blood sugar into cells to use as fuel and to store the rest in the muscles.
But if you eat a huge pile of French fries or a big piece of bread, your body has to deal with a serious flood of blood sugar, so it overreacts, pumping out too much insulin. If you’re overweight, it may pump out even more. All that extra insulin brings blood sugar down — too far. And it hangs around a long time, keeping your blood sugar low for hours. As a result, you can fall into a semi-starved state. Indeed, your blood sugar may be even lower than it was before you ate! Now you’re really dragging. Your energy is low. You may get a headache.
Your body recognizes that your blood sugar is too low, so it reverses course, spewing out hormones that raise blood levels of sugars and fats (the kind that could trigger a heart attack). Your brain also sets in motion signals that tell you that you’re hungry. Even though you ate more calories at lunch than you really needed, your blood sugar is so low that your body thinks it needs more food. Those doughnuts in the conference room sure look attractive right now.
It’s not just low blood sugar but also rapidly falling blood sugar that triggers a powerful hunger signal. In 16 studies, 15 of them found that meals that raise blood sugar quickly resulted in feeling hungrier before the next meal. For example, in a study of 65 women, those whose meals were designed to keep blood sugar stable reported feeling less intense hunger and less desire to eat, especially during the afternoon.
These kinds of meals increase levels of leptin, a hormone that decreases hunger (and boosts fat burning) and lowers levels of ghrelin, a hormone that increases hunger. The women who ate blood sugar-boosting meals reported that they felt hungrier sooner.
In many studies, people who ate such meals also ate more at the next meal. In a study of overweight teenage boys, the boys ate 500 more calories within 5 hours after eating blood sugar-boosting breakfasts and lunches than they did when they ate meals that were kinder to their blood sugar. In other studies, the differences were more modest, about 150 calories.
Still, eating even 100 extra calories a day may mean the difference between losing weight and gaining it.
Now, you can lose weight on any diet that cuts calories. But losing is only half the battle — and often, it’s the easiest part. Sticking to a healthy eating plan that lets you keep the weight off is the hard part. Eating plenty of Magic foods is a key solution.
When you eat a meal that really bumps up your blood sugar, your body pumps out lots of insulin to bring it down, as you’ve just learned. But it also stops burning fat for fuel so it can use up the blood sugar instead. Your belly (or butt or thighs) pays the price. People whose diets boost blood sugar the most tend to have more body fat, especially around the abdomen, the most dangerous place for it to accumulate.
Getting off the blood sugar rollercoaster can make losing that spare tire a lot easier. In studies involving everyone from obese men to pregnant women to children, a blood sugar–stabilizing diet led to more body fat loss (or, in the case of the pregnant women, less body fat gain during the pregnancy). In a cruel twist of fate, a diet that causes your blood sugar to spike and dive may even slow your metabolism. Compared to a diet that keeps blood sugar levels stable, it reduces the rate at which you burn calories when you’re sitting still. In a study of 39 overweight men and women, the difference worked out to about 80 extra calories burned each day. That’s an extra pound (0.5 kg) lost about every six weeks, or more than 8 pounds (3.5 kg) a year. The more overweight you are, the greater the difference may be.
It’s fairly easy to imagine how a diet that’s rough on your blood sugar can contribute to weight gain. It’s a little harder to understand how it can also contribute to a heart attack — yet it can. It can lead to clogged arteries and higher blood pressure, and it can raise the level of inflammation in the body, which doctors now know is intimately connected with heart attack risk.
High blood sugar produces unstable forms of oxygen called free radicals. These nasty molecules damage the arteries, making it harder for blood vessels to do their job of keeping blood pressure normal and making cholesterol more likely to stick like glue to artery walls.
The high levels of insulin that your body needs to tame all this blood sugar are pretty nasty, too.
They can set in motion changes that raise blood pressure, make blood more likely to form heart-threatening clots, and increase inflammation — all of which raise your heart disease risk. Over time, meals that cause blood sugar to spike also tend to lower “good” HDL cholesterol and raise triglycerides, fats that are toxic to cells, increasing the risk of heart disease — and of sudden cardiac arrest.
Big major studies have shown how powerful these damaging effects can be to the heart. In a study of more than 43,000 men age 40 and older, those whose diets boosted blood sugar the most were 37 percent more likely to develop heart disease in the following 6 years. In the Nurses’ Health Study of more than 75,000 middle-aged women, those whose diets boosted blood sugar the most were twice as likely to develop heart disease over 10 years. For overweight women, such a diet was even more threatening. For instance, their triglycerides were 144 percent higher than those of women who ate a healthier diet, compared to 40 percent higher for women who weren’t overweight.
Fortunately, the phenomenon works in reverse, too: The kinder your meals are to your blood sugar, the kinder they’ll be to your heart. Several studies have found that people who ate the fewest blood sugar–boosting foods had higher levels of HDL cholesterol, lower triglycerides, and fewer heart attacks.
It’s even harder to imagine how seesawing blood sugar levels could possibly lead to cancer, but high insulin levels seem to promote an environment that makes it easier for certain tumors to grow. Research is still ongoing, and, unlike with heart disease and diabetes, it’s too early to make strong statements about the connection between blood sugar levels and cancer. But there is cause for concern with the following cancers.
Colon and rectal cancer. In the Health Professionals Follow-up Study conducted by the Harvard School of Public Health and involving more than 50,000 middle-aged men, those whose diets were most likely to raise blood sugar fast and high were 32 percent more likely to develop colon or rectal cancer over 20 years. The heavier the men, the stronger the effect. In the Women’s Health Study, funded in part by the U.S. National Cancer Institute, the rise in cancer risk was an astounding 185 percent higher over 8 years.
Breast cancer. In the Women’s Health Study, sedentary women who followed a blood sugar–boosting diet were 135 percent more likely to develop breast cancer over seven years than women whose diets were more blood sugar friendly. These women had not yet entered menopause. On the other hand, a Canadian study of nearly 50,000 women found no link to breast cancer before premenopause, but among postmenopausal women, there was an 87 percent increase in breast cancer risk — and it was even higher if the women did little or no vigorous exercise. A Mexican study comparing women who got breast cancer with those who didn’t found the risk was 62 percent greater with blood sugar–boosting diets. A similar Italian study found an 18 percent increase.
Endometrial cancer. In the Iowa Women’s Health Study, which involved more than 23,000 postmenopausal women, those who didn’t have diabetes and followed blood sugar–spiking diets were 46 percent more likely to get this cancer over 15 years. An Italian study that compared women who developed endometrial cancer with a similar group of women who didn’t found a 110 percent increase in risk linked to this type of diet.
Prostate cancer. An Italian study looked at men ages 46 to 74 who developed prostate cancer and compared their diets with those of a similar group of men who didn’t get the cancer. Those whose diets were most likely to spike blood sugar were 57 percent more likely to have prostate cancer. A similar Canadian study found a 57 percent increase in risk.
Pancreatic cancer. Even the organ that produces insulin may be more prone to cancer if it’s constantly bathed in that hormone. A study using data from the Nurses’ Health Study over 18 years found that women whose diets raised blood sugar the most were 53 percent more likely to develop pancreatic cancer than women whose diets raised it the least. Women in the first group who were overweight and physically inactive were 157 percent more likely to get the cancer than similar women in the second.
A meal that raises blood sugar fast and furiously can leave you dragging like a willow in a windstorm. Not surprisingly, it doesn’t do much for your mood, either.
Our moods are intimately affected by the levels of hormones in our systems, including the hormone insulin. These hormones in turn affect neurotransmitters, chemical messengers in the brain. The different types of nutrients we eat, including carbohydrate and protein, affect these transmitters differently, triggering drowsiness or alertness. But the brain may be most sensitive to one simple compound: blood sugar.
Unlike muscles, the brain can’t store sugar. It needs just the right amount of it at all times to function best, so it’s not surprising that it’s very sensitive to even very small differences in the amount of blood sugar available. A steady supply — which the foods in this book will help you achieve — is by far the best.
Both low and high levels of blood sugar can cause trouble when it comes to your mood and memory. People report feeling more symptoms of depression when their blood sugar is low. Memory is affected, too. In one study, people with diabetes had more trouble processing information, remembering things, and paying attention — besides being in a bad mood — when their blood sugar was low. In people with type 2 diabetes, blood sugar swings are linked not only with poor memory but also, over time, with cognitive decline and dementia.
High blood sugar levels spell trouble, too. Long before they cause diabetes, they can impair the brain, shrinking a part that stores memories and increasing the risk of Alzheimer’s disease. In one study at New York University, researchers found that in people who tended to have high blood sugar levels after meals, a part of the brain called the hippocampus, which is most associated with long-term memory, was smaller than in people whose postmeal blood sugar levels were lower.
On the positive side, keeping your blood sugar on an even keel can help you feel better and stay mentally sharp. People with diabetes who control their blood sugar well report better moods, less depression, and less fatigue than those who don’t. Careful studies have found that the better they control their blood sugar, the better they are able to recall a paragraph after reading it and to remember words from a list.
In general, eating a good breakfast is the best way for anyone to improve mental functioning later in the day. Studies regularly show that eating breakfast improves mood, mental alertness, concentration, and memory. Eating the right breakfast, one that keeps blood sugar on an even keel until lunch, is likely to work even better.