New Findings on FiberMay 2005
By Stephen Laifer
Recent interest in the importance of including fiber in the diet belies the fact that nutritional specialists have advocated its benefits for more than half a century. Even before the fifth century BC, the Greek physician Hippocrates, often regarded as the father of Western medicine, recommended consuming fiber-rich natural foods. In 1953, nutritionist E. H. Hipsley introduced the term “dietary fiber” to represent intake of the indigestible components of plant cell walls.1
A more precise definition of fiber was established in 1969, as prevailing nutritional habits were linked with the prevalence of various diseases.2,3 In their study of traditional foods consumed by different cultures, Drs. Hugh Trowell and Dennis Burkitt noted that cultures with diets rich in plant foods rarely suffered from illnesses like diabetes, cancer, and cardiovascular disease.4 By contrast, these diseases had become widespread in developed Western societies in the late 1800s with the advent of a milling technique that produced a new, fiber-depleted dietary staple: white flour.3 Fiber, they therefore reasoned, might offer protection against many of the diseases prevalent in modern Western societies.
These early nutrition research findings have been borne out by countless subsequent studies. One recent study found that every additional 10 grams of fiber consumed on a daily basis cuts the risk of coronary heart disease death by 27%.5 Modern medicine recognizes fiber—the edible parts of plants that are resistant to digestion and absorption in the human small intestine—to be an essential component in maintaining a healthy body. Today, a growing body of research is examining one of fiber’s least-publicized benefits: its ability to help reduce caloric intake and thus maintain a healthy weight.
Controlling Weight, Preventing Disease
One of the most alarming health concerns of the last decade is explosive growth in the of number of people—especially younger people— who are overweight or obese. Processed foods and increasingly sedentary lifestyles exacerbated the problem throughout the twentieth century. By the turn of the millennium, obesity had already become epidemic in the US and other industrialized nations.6 Using standardized heights and weights, the 1999-2000 National Health and Nutrition Examination Survey (NHANES) estimated that 65% of American adults were overweight or obese.7 Being overweight or obese is associated with the increased risk or onset of afflictions such as atherosclerosis, coronary heart disease, and diabetes.
Modern science confirms that fiber can help maintain normal body weight by reducing food intake at each meal. The body processes a fiber-rich meal more slowly, which promotes feelings of fullness or satiety sooner. Fiber-rich food is also typically lower in calories, fat, and added sugars, and is thus less “energy dense” than other dietary choices. All these factors help create a dietary pattern that can be beneficial in preventing or correcting undesirable weight gain.
A study by the Dutch Animal Sciences Group found that dietary fiber stabilized glucose and insulin levels in sows on restricted diets several hours after feeding. The animals’ behavior indicated that increased fiber intake promoted a prolonged feeling of satiety.8 Dietary energy density was the focus of another series of long-term studies designed to prove that diets low in energy-dense foods promote weight loss. In studies lasting longer than six months, weight loss was more than three times as great in people eating low-fat, high-fiber diets than in those eating diets low in fat only.9
A 1997 study investigated the effects of one week of supplementation with guar gum (a water-soluble fiber) on hunger and satiety, as well as calorie intake, in obese test subjects. Adding fiber to the diet decreased food intake, and subjects on a reduced-calorie diet reported diminished hunger after supplementing with fiber. Thus, fiber may assist in weight-management programs by promoting a feeling of fullness, decreasing hunger, and promoting adherence to a reduced-calorie diet.10
Another study confirmed these effects. When overweight individuals added 14 grams of fiber daily to their otherwise unrestricted diet, they consumed 10% fewer calories. This led to an average of 4.2 pounds of weight loss in just under four months.11
Research also indicates that energy density and macronutrient composition may be more important than caloric intake in diets that contribute to obesity.12 Usually, foods that are rich in dietary fiber are relatively low in fat and contain components that are primarily indigestible. A diet that provides energy from proteins, vitamins, minerals, and fibers can help lower fat intake and assist in maintaining or improving body weight. These factors are especially important in treating obesity in children, according to the Department of Pediatrics at Harvard Medical School, which notes that modern nutritional research indicates an important role for fiber in regulating body weight.13
Calcium Complements Fiber’s Effects
While weight loss is associated with myriad benefits for health and longevity, one potentially negative effect of losing weight is that it often reduces bone mass and increases the risk of fracture. In fact, researchers have hypothesized that during periods of weight loss, the body’s calcium requirement increases.20 Diets rich in protein and calcium may protect against bone loss during weight reduction.21
Calcium not only helps protect bone health during weight loss, but also assists in weight loss. Calcium can actually increase the rate of weight and fat loss during caloric restriction. In a 24-week study of obese adults on a calorie-restricted diet, those on a diet high in calcium or dairy foods lost more weight and body fat than those on a standard diet. In addition, more abdominal fat was lost in the calcium and dairy groups.22
A recent study shed some light on how calcium may promote weight loss. Calcium may help reduce body weight by binding to fat in the intestine and increasing its excretion from the body.23 Danish researchers demonstrated a 2.5-fold increase in the amount of fat measured in fecal matter after calcium supplementation.23
Some studies show a stronger weight-loss effect from dairy calcium than from supplemental calcium. This may be due to other components of dairy products that promote optimal body composition, such as branched-chain amino acids and whey protein.24 Epidemiological and clinical trials indicate that diets that include three or more daily servings of dairy products result in significant reductions in fat tissue mass in obese adults, even in the absence of caloric restriction. When included in a calorie-restricted diet, dairy foods markedly accelerate weight and body fat loss.24
Calcium’s other health-promoting benefits may include improving cardiovascular health by lowering blood pressure and raising levels of beneficial HDL (high-density lipoprotein). Additionally, calcium has been shown to help prevent colon polyps and to reduce the recurrence of kidney stones.25
Lowering Cholesterol and Triglycerides
Heart disease is one of the leading causes of mortality in the Western world. Because heart disease is linked to obesity, cardioprevention through dietary means has until recently focused almost exclusively on reducing intake of cholesterol and fat. More recent research, however, shows an important link between enhanced cardiovascular health and greater intake of fruits, vegetables, and whole grains.26 The protective effect of plant-based foods has been ascribed in large part to their fiber and phytochemical content.
Indeed, fiber’s ability to reduce the risk of developing and dying from coronary heart disease was among the earliest findings of dietary fiber research.27,28 A subsequent 12-year study of 859 southern California men and women upheld this finding, showing that a 6-gram increment in daily fiber intake was associated with a 25% reduction in ischemic heart disease mortality.29
Since that landmark long-term study, researchers have delved further into the effects of greater dietary fiber consumption on coronary heart disease risk. A 1999 study in Finland, for example, concluded that high intake of fiber and cereal products was associated with lower levels of serum cholesterol in coronary patients who were not using lipid-lowering medication.30 Two types of fiber in particular—beta glucan (in oats) and psyllium husk—have been so thoroughly studied that the FDA has authorized a health claim that foods containing 0.75 or 1.7 grams of soluble fiber per serving, respectively, can reduce the risk of heart disease.31
High levels of cholesterol and LDL are accepted as risk factors for heart disease. Dietary fiber helps to reduce cholesterol by binding to cholesterol-laden bile excreted from the liver into the small intestine. This reduces the re-absorption of bile into the bloodstream and thus helps to lower total cholesterol, LDL, and serum triglyceride levels simultaneously.32
Triglycerides are the compounds in which fat moves through the bloodstream. People who have high levels of potentially harmful LDL and low levels of beneficial HDL often have high triglycerides.
Elevated triglyceride levels are increasingly associated with increased risk for heart disease.33,34
Fiber affects another heart disease risk factor known as C-reactive protein (CRP). Elevated CRP levels are associated with an increased risk of heart disease. A 2004 study by the federal Centers for Disease Control and Prevention examined the link between dietary fiber and CRP serum concentration. Using data from 3,920 participants aged 20 and older, the researchers found that increased fiber intake was associated with lower levels of CRP.35 In fact, the risk of increased CRP concentration was almost halved for those with the highest fiber intake. Thus, fiber favorably influences numerous risk factors for cardiovascular disease, and may help to minimize or eliminate the need for potentially dangerous prescription drugs for cardiovascular health.