Peruse the aisles of your local supermarket and you’re likely to find low-fat versions of just about everything. Lighter versions of chips, dips, yogurts, and even peanut butters have been popping up on shelves for over three decades. But could the longstanding beliefs about the heart-healthy benefits of low-fat diets actually be wrong?
Fat has been considered somewhat of a dietary villain for almost 40 years in the US. In 1977, US public officials implemented guidelines restricting fat consumption to no more than 30 percent of daily calorie intake, based on the notion that the macronutrient is detrimental to heart health. The UK followed suit with similar recommendations in 1983.
But a recent meta-analysis indicates that the recommendations may have been based on false information, and the researchers believe that the “dietary advice not merely needs review; it should have not been introduced.” This isn’t the first time the original guidelines have been called into question. The 2014 documentary “Fed Up” featured a panel of health experts arguing that sugar—rather than fat—is the bigger culprit in America’s obesity epidemic, and another recent study published in the Annals of Internal Medicine indicated that saturated fat isn’t as harmful to the heart as we originally thought.
The new research
Researchers examined six clinical trials that reviewed the relationship between dietary fat, cholesterol levels, and heart disease that influenced the original recommendation. The trials followed 2,400 men (no women). The researchers discovered the following:
- A low-fat diet had no impact on heart disease. There were no differences in death rates between the men who ate low-fat diets and those who didn’t; the groups were equally likely to die of heart disease.
- Lower-fat diets did not reduce deaths from any cause. One group that limited its saturated fat to 10 percent actually had more deaths from heart disease and other causes than those who didn’t.
- Lower-fat diets did impact cholesterol levels. Men who ate less fat had lower cholesterol but were not less likely to die from heart disease or other causes (however, large trials have shown that lowering cholesterol is important in lowering the risk of cardiovascular disease).
- The participants did not follow universal guidelines. Only one of the studies had participants follow the current guidelines (30 percent of daily calories from fat and less than 10 percent from saturated fat). The other studies used different approaches.
When the US and UK implemented the guidelines, neither cited any randomized controlled studies (RCTs) available at the time. RCTs, which involve studying a sample randomly assigned to one treatment or another, are considered the gold standard for clinical trials and used to test the efficacy of various types of medical interventions.
Could cutting saturated fat be bad?
Some experts believe that cutting fat leads to the overconsumption of refined sugar, which many have argued has led to the profound increase in diabetes rates. While there were zero documented cases of Type 2 diabetes in 1980, there were nearly 60,000 in 2010. And according to “Fed Up, ” some low-fat products contain twice the sugar of the original full-fat versions, which manufacturers add to compensate for the lack of flavor.
The low-fat craze has also led to the introduction of more trans fats—considered by many health experts to be the most unhealthy dietary fat—to replace saturated fats. Most trans fats are formed by adding hydrogen to vegetable oil, a process that causes the oil to become solid at room temperature and decreases the likelihood of spoilage. But the long shelf life comes at a cost: Trans fats raise LDL (“bad”) cholesterol and lower HDL (“good”) cholesterol, increasing the risk of heart disease. The good news is that the FDA is taking steps to remove artificial trans fats from the food supply. Food manufacturers must stop using trans fats within the next three years.
What does this mean for me?
Although the study offers compelling insight into the potential shortfalls of the current dietary recommendations, it has some limitations. Chief among them is the question of whether the design of the trials—none of which was an RCT—impacted the validity of the current guidelines. Although RCTs are considered the ideal research method in drug trials, they aren’t as reliable in the development of nutrition guidelines.
“Nutrition studies are notoriously hard to run,” acknowledges One Medical Group’s Malcolm Thaler, MD. Drug trials involve participants who are likely to benefit from the drug being tested, and the results are used to benefit a similar population. Dietary research, on the other hand, is usually performed on people with particular diseases, and the results are intended to target a healthy population. Cost, commitment, and the ambiguity of reliability create unique challenges in conducting RCTs on healthy participants, and extrapolating the results from a particular set of people to the general population may not be ideal, anyway.
Currently, experts still disagree on how much fat is best to include in a diet designed for heart health, and more research is needed. The American Heart Association still backs a low-fat approach, recommending 25 to 35 percent of daily calories come from fat, and no more than 7 percent from saturated fat. And most health experts advocate a moderate fat diet, including the standard 30 percent of calories from fat, but replacing saturated fat with healthier fats like vegetable oils.
“What we do know is that it’s best to keep things simple,” says Thaler. “The Mediterranean Diet, high in fiber, fruits, vegetables, nuts, olive oil, and fish, has been shown to be healthful and to prolong life compared to other ways of eating. And it encourages you to wash it all down with a glass of wine!”