Carbohydrate Confusion
Carbohydrate-rich foods, once the staple that most people turned to for weight loss and overall good health, are now cast in the role of dietary demons by the gospel of low-carb diets. The tremendous surge in popularity of the Atkins, South Beach, and other related diets has led millions of people to turn away from this dietary mainstay.
The low-carb fad notwithstanding, carbohydrate-rich foods still form the foundation of what most people eat. The average American gets about 50 percent of his or her energy from carbohydrates, 33 percent from fat, and 17 percent from protein. Good sources of carbohydrates include bread, pasta, fruits and vegetables, and whole grains.
Why Bother with Carbohydrates?
There are four main reasons to eat foods that deliver a lot of carbohydrates:
- Cost. Grains, vegetables, and fruits generally cost much less per pound than protein.
- Availability. In almost every culture, farmers and foragers focus on grains, vegetables, and fruits.
- Taste. Carbohydrates offer tastes that range from the high, bright note of an apricot to the mellow taste of barley and the summery pop of zucchini.
- Health benefits. Choose wisely: Consuming plenty of fruits, vegetables, and whole grains can reduce incidences of heart disease, type 2 diabetes, some cancers, and other common chronic conditions. (Hu and Willett, JAMA, 2002 and Slavin, Proceedings of the Nutrition Society, 2003)
What's Simple is Really Complex
Carbohydrates have traditionally been divided into two main groups—simple carbohydrates (sugars) and complex carbohydrates (starch and fiber). For many years experts recommended we eat plenty of complex carbs and go easy on sugars. Unfortunately, the carbohydrate story is far more complicated than this. The body turns some so-called complex carbohydrates into blood sugar every bit as fast as it does pure sugar. This is important because the body pays constant attention to blood sugar. As the level rises above a predetermined steady state, the body takes steps to pack that circulating sugar into muscle and fat cells. As the level threatens to drop below the steady state, the body taps into its energy stores to make sugar.
The distinction between "simple sugar" and "complex carbohydrate" has little biological significance. A better way to classify carbohydrate-rich foods is by their actual effects on blood sugar and insulin, the hormone that signals cells to absorb sugar from the bloodstream. Something called the glycemic index does just this. This is a relatively new way of ranking foods by how high equal and predetermined amounts boost blood sugar. Easily digested carbohydrates, such as grocery store white bread or white rice, boost blood sugar and insulin levels fast and high. Slowly digested carbohydrates, such as whole-grain bread or brown rice, have lower, slower effects on blood sugar and insulin. The related glycemic load indicates blood sugar and insulin changes that follow eating a usual portion of a food.
An intriguing theory is that eating foods that quickly boost blood sugar can lead to a relatively rapid return of hunger, while eating foods that have more gentle effects on blood sugar and insulin help you feel full or satiated longer.
What Carbohydrate Packages are Healthiest?
We get carbohydrates from four main sources: fruits, vegetables, grains, and beans. Is one source of carbohydrate just like another, or does it matter where you get your carbs?
Although this is a relatively new question, an answer is emerging from the gradually accumulating pile of evidence.
| Carb "type" | Energy density | Processing | Fiber | Glycemic index | Ideal dietary factor | |
|---|---|---|---|---|---|---|
| Fruits | Simple | Low | Low | High | Low | Yes |
| Vegetables | Complex | Low | Low | High | Low | Yes |
| Beans | Complex | Low | Low | High | Low | Yes |
| Whole grains | Complex | High | Low | High | Low | Yes |
| Refined grains | Complex | High | High | Low | High | No |
| Potatoes | Complex | Low | Low | Low | High | No |
Evidence for Beneficial Health Effects of Fruits
Blood pressure
In a seven-year study of 1,710 initially healthy men, systolic blood pressure (the upper number of a blood pressure reading) was an average of 2.2 points lower among men who ate half a cup or more of fruit per day. (Miura and colleagues, American Journal of Epidemiology, 2004)
Stroke
A four-year follow-up study of 50,000 Danes demonstrated that those in the top fifth of fruit consumption had a 40 percent lower risk of the most common kind of stroke (an ischemic stroke, caused by a clot blocking an artery supplying the brain with oxygenated blood) compared to those in the bottom fifth. This effect was seen for most categories of fruit. (Johnsen and colleagues, American Journal of Clinical Nutrition, 2003)
Cancer
A remarkable 60-year study of 5,000 men and women showed that individuals who were in the top fifth of fruit consumption during childhood had a 38 percent lower risk of cancer during adulthood compared to those in the bottom fifth. In this study, other dietary factors were not linked with cancer risk. (Maynard and colleagues, Journal of Epidemiology and Community Health, 2003)
Eye disease
Among 100,000 men and women followed for 12-18 years, individuals who reported consuming three or more cups of fruit a day had a 36 percent lower risk of age-related degeneration of the eye's macula than did those who reported eating less than 1.5 cups per day. In this study, no other dietary factors beside fruit consumption were associated with risk. (Cho and colleagues, Archives of Ophthalmology, 2004)
Evidence for Beneficial Health Effects of Vegetables on Heart Disease
In an eight- to 14-year follow-up of 100,000 adults who filled out detailed dietary questionnaires, the risk of coronary heart disease decreased by 23 percent for every extra serving of green leafy vegetables per day. (Joshipura and colleagues, Annals of Internal Medicine, 2001)
Life expectancy
In a 30-year study of 1,500 rural Italians, men who ate more than 60 grams of vegetables a day lived an average of two years longer than men who ate less than 20 grams a day. The beneficial effect of vegetables was especially strong for smokers. (Seccareccia and colleagues, Annals of Epidemiology, 2003)
Type 2 diabetes
In a survey of more than 1,000 middle-aged men and women, those who reported frequently eating vegetables were 86 percent less likely to develop diabetes than those who didn't routinely eat vegetables. (Williams and colleagues, Journal of Clinical Epidemiology, 1999)
Breast cancer
European researchers pooled the results of 17 studies that examined the effect of vegetable consumption on breast cancer between 1982 and 1997. Women in the top tier of vegetable consumption were 25 percent less likely to have breast cancer than those in the lowest tier. In this study, vegetables had a stronger impact on breast cancer risk than any other dietary factor. (Gandini and colleagues, European Journal of Cancer, 2000)
Prostate cancer
A comparison of 600 men under age 65 with prostate cancer and 600 similarly aged men without the disease showed that men who ate at least 28 servings of vegetables a week (four a day) had a 35 percent lower risk of prostate cancer than men who ate under 14 servings a week (two a day), lowering the risk of prostate cancer by 35 percent. Cruciferous vegetables such as broccoli, cauliflower, cabbage, Brussels sprouts, and kale appeared to have the strongest anti-prostate cancer effect. (Cohen and colleagues, Journal of the National Cancer Institute, 2000)
Evidence for Beneficial Health Effects of Beans (Legumes) and their Effects on Cardiovascular Risk Factors
After pooling the results of 11 studies of the health effects of eating beans other than soybeans, researchers found that increased intake of beans:
- Lowered LDL (bad) cholesterol about six percent.
- Raised HDL (good) cholesterol about three percent.
- Lowered triglycerides (the main fat-carrying particle in the bloodstream) almost 17 percent. (Anderson and Major, British Journal of Nutrition, 2002)
Effects on diabetes control
Effects on other conditions
Beans and other legumes may also protect against:
- Prostate cancer
- Osteoporosis (Messina, American Journal of Clinical Nutrition, 1999)
Evidence for Beneficial Health Effects of Grains and Effects on Heart Disease
In an eight-year study of 3500 initially healthy adults over age 65, those with the highest daily fiber intake had a 21 percent lower risk of heart disease and stroke. (Mozaffarian and colleagues, Journal of the American Medical Association, 2003)
Effects on body weight
A 12-year study of 75,000 initially healthy women found that weight gain was more likely to have occurred among women who ate more refined grains and less likely to have occurred among women who ate more whole grains. Women in the highest category of daily fiber intake had a 49 percent lower risk of excessive weight gain. (Liu and colleagues, American Journal of Clinical Nutrition, 2003)
Effects on mortality
In a study of 86,000 initially healthy men, those in the highest category of whole grain intake were 17 percent less likely to have died over the five-year course of the study. Those in the highest category of refined grain intake weren't protected against dying. (Liu and colleagues, American Journal of Clinical Nutrition, 2003)
Effects on diabetes
Among 42,000 men, those in the highest category of whole grain intake had a 48 percent lower risk of developing type 2 diabetes during the 12-year study. Eating high levels of refined grains didn't offer similar protection. (Fung and colleagues, American Journal of Clinical Nutrition, 2002)
Effects on cancer
In a study comparing 250 men and women with cancer and 250 without it, researchers found that individuals in the highest category of whole grain intake were 30 to 70 percent less likely to have developed cancers involving the upper gastrointestinal tract than those in the lowest category of whole grain intake. At the same time, those in the highest category of refined grain intake were two to four times more likely to have developed cancer than those in the lowest category of refined grain intake. (Levi and colleagues, European Journal of Clinical Nutrition, 2000)
Evidence for the Health Effects of Potatoes and their Effects on Stroke
In a 14 year study of 75,000 initially healthy women, every major category of fruits and vegetables provided protection against ischemic stroke, with one notable exception—potatoes. (Joshipura and colleagues, Journal of the American Medical Association, 1999)
Effects on type 2 diabetes
An in-hospital study compared two diets that were identical except for their inclusion of rice and potatoes. Eight volunteers with type 2 diabetes ate each diet for a week and then switched to the other. On the potato-containing diet, levels of LDL (bad) cholesterol, triglycerides, and the formation of bile acids (a precursor of cholesterol) were all worse than they were on the rice-containing diet. (Andersen and colleagues, American Journal of Clinical Nutrition, 1984)