Type-2 diabetes used to be called adult onset diabetes because it occurred primarily in older people, but we are beginning to see it at astounding rates among teens and even children in the United States.
Some people with type-2 diabetes take medication, but the condition can often be managed very well through diet and exercise. Sometimes, losing a few pounds is enough to improve glucose control. There are a number of reasons why a diet based on whole plant foods could be helpful for controlling diabetes:
• A vegan diet doesn’t guarantee that you’ll be slender, but vegans are less likely to be obese. Weight loss is often the single most effective way to control diabetes.
• Although vegan diets are typically high in carbohydrates, they tend to have a low glycemic index, which could be an advantage in controlling diabetes. The glycemic index is a measure of how quickly carbohydrates are digested and absorbed. We’ll discuss this further later in the chapter.
• People with diabetes are at especially high risk for cardiovascular disease. So the factors in plant-based diets that reduce risk for CVD can be especially important for those with diabetes.
• The lower rates of hypertension in vegans can be important, too, in controlling some of the complications of diabetes.
Dr. Nathan Pritikin was an early advocate of a vegan diet that limited all fats. His approach was effective in reducing cholesterol, blood sugar, and blood pressure levels.
A few years later and using a similar although not-quite-vegan diet, Dr. Dean Ornish launched a study called the Lifestyle Heart Trial.
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The subjects were people with moderate to severe coronary heart disease. Some followed the usual diet that was recommended for heart disease and others adopted a comprehensive lifestyle plan which included a 10 percent fat vegetarian diet (consisting almost entirely of whole plant foods with the addition of nonfat dairy), aerobic exercise, stress management, support groups, and smoking cessation.
The subjects who followed a standard cholesterol-lowering plan actually got worse over the course of the study (atherosclerosis increased by nearly 28 percent after five years), but the health of subjects in the lifestyle group improved. Atherosclerosis in this group decreased by nearly 8 percent after five years.
More recently, researchers with the Physicians Committee for Responsible Medicine (PCRM) looked at the effects of a low-fat vegan diet on type-2 diabetes.
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Subjects in the test group were instructed to follow a low-fat vegan diet based on whole plant foods with no limits on carbohydrates, calories, or portion sizes. Those in the control group followed a typical American Diabetes Association (ADA) diet, which uses portion control and carbohydrate counting and includes animal foods.
With their higher carbohydrate intake, it might seem like those on the low-fat vegan diet would get worse, but they didn’t. They lost
more weight, even though they didn’t count calories or measure their food, and their blood glucose was better controlled.
These effective approaches for reversing heart disease and controlling diabetes have two things in common. First, they are based on whole plant foods rather than refined carbohydrates. And second, they are very low in fat—as low as 10 to 15 percent of calories in some cases.
It’s likely that many of the benefits of these diets are explained by weight loss (which reduces blood cholesterol), reduced intake of saturated fat, and perhaps protective compounds in plants. It may be that simply eating a vegan diet—based mostly on whole, unprocessed foods—and reducing calorie intake is enough to achieve therapeutic results. We’ll see below that whether or not these diets need to be low in total fat is an issue of much debate.
FAT AND CHRONIC DISEASE
Reducing intake of saturated fat is important for reducing LDL-cholesterol levels, but it’s possible that including some higher-fat plant foods in the diet is better for managing disease. In Chapter 12, we talked about the ideal cholesterol profile for reducing heart disease: low LDL-cholesterol and high HDL-cholesterol. When all types of fat in the diet are replaced with mostly carbohydrates, both LDL-and HDL-cholesterol drop.
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But replacing saturated fat with healthful plant fats lowers LDL-cholesterol without affecting the good HDL-cholesterol. Monounsaturated fat also improves glucose control in people with diabetes when it replaces saturated fat or carbohydrates in the diet.
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This has led some researchers to conclude that the healthiest diet is one that is very low in saturated fat but not too low in total fat.
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The traditional Mediterranean diet is an example of a healthful eating pattern that includes good fats, especially the monounsaturated fats found in nuts, olives, and avocado.
How much this matters for people following vegan diets is still up for debate. But low HDL levels seem to be an important risk factor for women in particular and for those with type-2 diabetes.
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HDL levels also matter a great deal for people who are overweight and sedentary. For example, in the EPIC-Norfolk study, the ratio of total cholesterol to HDL-cholesterol was more strongly linked to heart disease risk than LDL levels.
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Some nutritionists believe that people who cook with olive oil, which is rich in monounsaturated fat, are likely to consume more vegetables (because the olive oil makes them taste so good). So it may be that vegetables are the protective factor and olive oil is just an innocent bystander. But olive oil also contains compounds that affect blood-clotting factors associated with heart disease risk.
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This suggests that small amounts of olive oil could be beneficial—or at the very least not harmful. While nobody knows exactly how much fat is ideal, it seems clear that a very low-fat diet is not the answer for everyone who needs to reduce disease risk.
Another type of fat in foods—trans fats—should definitely be avoided.
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Although small amounts of trans fats are found naturally in foods, most comes from processed foods made with partially hydrogenated fats. Hydrogenation is the process that turns vegetable oils into solid fat. Consuming trans fat raises the levels of bad LDL-cholesterol, reduces protective HDL-cholesterol, and is associated with a higher risk of both heart disease and diabetes. The American Heart Association recommends limiting trans fat to 1 percent of total calories. That’s such a tiny amount that practically speaking, it means you should just avoid all foods that list “partially hydrogenated” oils on the label. (If the label says “fully hydrogenated” or “hydrogenated,” the fats have been turned into saturated, not trans, fats. And it’s still a good idea to avoid saturated fats.)
Although the amount of trans fat in a food must be listed on the label by law, if the amount is less than ½ gram, the label can say that the food contains “0” grams of trans fat. Since the upper limit for trans fat
intake on an 1,800-calorie diet would be two grams per day, eating foods with small amounts of trans fat can add up quickly.
THE GLYCEMIC INDEX: HOW CARBOHYDRATES AFFECT DISEASE RISK
Carbohydrates are digested and absorbed into the bloodstream as glucose, sometimes called blood sugar. When glucose levels rise, the hormone insulin is released into the blood. Insulin helps cells absorb fat and glucose from the blood, allowing the cells to use these nutrients for energy. Some carbohydrates are converted to glucose more gradually than others. The glycemic index (GI) is a measure of how quickly carbohydrates are broken down and absorbed into the blood. A meal with a high GI causes a surge in the release of insulin, which is associated with increased risk for CVD, diabetes, and possibly cancer.
Foods with a low GI can help with weight control since they help promote the use of body fat for energy, and they also tend to be more satisfying.
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Diets that are very high in protein are based on the idea that carbohydrates—because of their effects on insulin—are responsible for weight gain. But vegans are typically closer to their ideal body weight than omnivores, despite their higher carbohydrate intakes. And the PCRM studies showed that people on very high carbohydrate diets lose weight and have better blood-glucose control.
The key is to choose carbohydrate-rich foods with low GIs, which means eating more unprocessed, whole plant foods in place of refined carbohydrates. Most types of processing seem to affect the GI. For example, while beans typically have a low GI, the index tends to rise the longer the beans are cooked. And grinding grains into flour increases the GI. The amount of fiber in a food affects its GI, but other factors, some of them fairly obscure, are even more important.
In fact, sometimes the glycemic index makes no sense. Because the type of starch in a food impacts its GI, pasta made from white flour actually has a lower GI than brown rice.
And the glycemic index doesn’t always tell the whole story about the effects of a food on blood glucose. Some foods have a high GI, but they contain so little carbohydrate that it doesn’t matter. Carrots are a prime example.
Finally, foods that are high in the simple sugar fructose—including table sugar—have a relatively low GI. But some research suggests that a large amount of fructose in the diet is linked to obesity, heart disease, diabetes, and high blood pressure. When it comes to added sweeteners, a good rule of thumb is to minimize all of them regardless of their GI.
Despite these quirks, it’s fairly easy to make healthy food choices to keep the GI low in your meals.
REDUCE THE GLYCEMIC INDEX OF MEALS WITH EASY REPLACEMENTS
Choose these foods . . .
| More often than these...
|
|---|
Bread made from unground whole, cracked, or sprouted grains (sometimes called “grainy” bread)
| Breads made from flour
|
Sweet potatoes
| White potatoes
|
Whole potatoes cooked in their skin
| Mashed potatoes
|
Spaghetti, oats, and barley
| White rice
|
Rolled oats or muesli
| Ready-to-eat or instant cereals
|
Whole raw fruits
| Juice or cooked or dried fruits
|
Raw or lightly steamed vegetables
| Canned or thoroughly cooked vegetables
|
Regular full-fat soymilk
| “Lite” or reduced-fat soymilk
|
Beans cooked from scratch
| Canned beans
|
Foods flavored with acidic ingredients, such as lemon or lime juice, vinegar, and tomato sauce
| Foods flavored with sweet sauces
|
Nuts and seeds
| Snack chips
|
Meals with small amounts of added fat and high-protein foods like tofu and tempeh
| Low-fat, low-protein meals
|
It doesn’t matter whether you need to reduce heart disease risk or control diabetes, the guidelines on how to eat are generally the same. For many people, simply losing weight and getting regular exercise is all it takes. Here are some other dietary changes that are important.
• Reduce your saturated fat intake. Vegans are automatically off to a good start in this regard, since most plant foods are naturally low in saturated fat. (The type of saturated fat in coconut oil appears to be less harmful than other types, but all added fats should be used in moderation.)
• Replace some of the saturated fat in your diet with foods that are rich in monounsaturated fats—olive and canola oil, olives, avocadoes, and nuts. These foods help lower LDL-cholesterol without reducing protective HDL-cholesterol.
• Include one to two servings of nuts in your daily menu since they have been shown to reduce LDL-cholesterol and have other heart-healthy factors.
• Avoid trans fats. They are found in any food that lists “partially hydrogenated” vegetable oil or fat on the label. Some brands of vegan cream cheese may contain partially hydrogenated oils.
• Increase your intake of whole, fiber-rich plant foods rather than refined carbohydrates.
• You don’t need to eliminate foods with a high GI from your diet, but it may help to emphasize foods with a low glycemic index (refer to the chart on page 186).
• It may be a good idea to include soyfoods in your diet since soy protein has been shown to reduce cholesterol levels.
• Reduce sodium intake if you have hypertension. Not everyone is salt-sensitive, but a diet high in salt is frequently related to high blood pressure, and it can also have a negative impact on bone
health. Getting enough potassium is just as important as reducing sodium intake for managing blood pressure. The best sources of potassium are carrot, orange, and tomato juices, white beans, lentils, sweet potatoes, spinach, Swiss chard, beet greens, sea vegetables, potatoes, dried fruit, and tomato sauce.
• Eat plenty of fruits and vegetables since these foods are high in antioxidants, which appear to protect against a number of diseases.
• Make sure you are meeting the requirements for omega-3 fats as discussed in Chapter 5.
• Talk to your doctor about alcohol. Moderate intake can help raise the good HDL-cholesterol. But for women, even low levels of alcohol consumption can put them at a higher risk for breast cancer.
• Keep in mind that specific needs and recommendations vary depending on your particular health issues. These are general guidelines that can help most people manage CVD and type-2 diabetes, but they may not be right for everyone.
Ounce for ounce, fat has twice the calories of protein or carbohydrate. Advocates of very low-fat diets note that the less fat you eat, the fewer calories you are likely to consume and the slimmer you will stay. Some people find that adopting a low-fat diet helps them lose weight without having to count calories or measure food intake. But for long-term weight control, there is evidence that including
some
higher fat foods in menu plans is helpful. When researchers compare weight loss on diets with different levels of fat, some subjects feel that the higher-fat diets are more satisfying.
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Eating a little bit of fat—usually in the form of nuts or nut butter—can make it easier to stick to a lower-calorie diet over the long-term.