Information and controversies about dietary fat abound on websites, in the news and in scientific journals. Should you avoid it? Should you eat it? How much? How often? What type and from what source? It can be hard to keep up with all the data and advice. But health researchers do appear to be clarifying their understanding of how dietary fat affects human health.
History
Dieters have been trying to avoid fatty foods since at least the late 19th century. In the 1940s, scientific evidence emerged linking high-fat diets to heart problems, and doctors began recommending low-fat diets to high-risk patients. In the 1960s, this nutritional advice made its way not just to people with health problems, but to anyone who wished to lose a few pounds. By the end of the 1980s, low-fat recommendations dominated health and weight-loss advice. Approaching 2011, however, increasing evidence points toward a vindication of fat, allowing it again a prominent role in a healthy diet.
Sources and Types
Sources of dietary fat include meat, fish, dairy products, eggs, nuts, coconut, avocado, tofu, chocolate, oils and the foods made from these ingredients. Not all these foods, however, contain the same type of fat. Meat, cheese and eggs tend to be high in saturated fat while fish and plant fats, such as tofu and nuts, tend to be high in unsaturated fat. Processed foods can contain trans fats, which are lab-altered plant oils sometimes listed as partially hydrogenated oil on a food label. Experts agree that if there's a problem with fat, it lies with saturated and trans fat, not unsaturated fat. In fact, increasing evidence indicates that unsaturated fat -- especially the omega-3 fatty acids found in cold-water fish, nuts and tofu -- provide health benefits.
Considerations
Three decades of data show that animal products are not always high in saturated fat, according to Nutrition Journal. Allowing animals to naturally graze on grass results in dairy, meat and egg products that are lower in both saturated fat and overall fat. They also contain more healthful omega-3 fatty acids. To purchase these products, look for labels that indicate the farm animals were pastured or grass-fed and grass-finished.
Key Studies
The Women's Health Initiative Dietary Modification Trial has provided fuel for those who challenge the anti-fat movement. The study, the biggest of its kind with 49,000 participants, found that a low-fat diet did little to prevent heart disease and certain types of cancers. Critics of the study, however, question these results because only 31 percent of the participants assigned to the low-fat plan actually adhered to its strict dietary guidelines. The study also failed to distinguish between saturated and unsaturated fat. Other studies, such as the Lyon Diet Heart study, have found that diets low in saturated fat but moderately high in unsaturated fats do provide health benefits.
Recommendations
Popular low-fat diets, such as the Dean Ornish plan, recommend a total fat intake of no more than 10 percent of daily calories. The American Heart Association and the 2010 USDA guidelines recommend a diet that consists of 20 percent to 35 percent fat, with no more than 10 percent of calories coming from saturated fat. Previous guidelines placed the upper limit at 30 percent. The science-based USDA guidelines are updated every five years and influence the recommendations of many other organizations.
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