Which Diets Really Raise Your Life Span? Two Come Out on Top
People at risk of heart disease could extend their lives by going Mediterranean or low-fat, according to a new analysis of popular diets.
In the world of nutrition and disease, dietary fat is an often confusing subject. And in general, experts say, recent years have seen a move away from prescribing a strict amount of dietary fat, and more focus on the source of that fat: Is it from healthful foods like olive oil and nuts, or from burgers and fries?
Still, the new analysis found some wins for low-fat eating.
Across 40 published clinical trials, those that tested low-fat diets showed that they helped prevent heart attacks and premature deaths among people at elevated risk. That included people who'd already suffered a heart attack or stroke, and those with conditions like high blood pressure, diabetes and obesity.
Low-fat diets were, at least, better than making no diet changes.
However, the benefits were even greater for people in trials of the famous Mediterranean diet — high in fish, vegetables and, yes, olive oil and nuts. The diet helped people live longer, and it not only lowered their risk of heart attack, but stroke as well.
Experts said the findings, published online recently in the medical journal BMJ, support what has become the common diet mantra in recent years: Eat more fish and plant-based foods, and limit red meat and processed foods.
"This supports what we have seen over the last couple of decades — that an eating pattern that focuses on more plant foods and less animal fat, like the Mediterranean diet, seems to help in the prevention of cardiovascular disease," said Connie Diekman, a St. Louis-based nutrition consultant and past president of the Academy of Nutrition and Dietetics.
Diekman, who was not involved in the study, said other evidence shows it's the source of the dietary fat that matters.
Fat from plant sources, like vegetable oils and nuts, is generally of the unsaturated variety, which may support heart health. Then there is oily fish, like salmon and bluefin tuna, which contain omega-3 fatty acids: Studies have found that those unsaturated fats can reduce the risk of early death among people with known heart disease.
At the opposite end of the spectrum are artificial trans-fats, which are found in many processed and commercially prepared foods. They appear on ingredients lists as "partially hydrogenated" oils. Trans fats can raise LDL ("bad") cholesterol while lowering the HDL ("good") kind, and they have been linked to an increased risk of heart disease.
It's clear those fats should be limited, said Theresa Gentile, a registered dietitian based in New York City.
But beyond that, it's important to think about overall diet quality, said Gentile, who is also a spokesperson for the Academy of Nutrition and Dietetics.
She noted that study participants on low-fat diets probably were not eating a lot of red meat, butter or other animal products — which could be beneficial, depending on what is replacing those foods.
You don't want the substitute to just be bagels and pasta, Gentile said.
The findings are based on an analysis of 40 clinical trials involving more than 35,000 participants in all. The trials tested the effects of seven different dietary programs, sometimes involving other lifestyle changes like exercise and smoking cessation.
Overall, only the Mediterranean diet and low-fat diets proved effective in cutting people's risk of heart complications or death.
Among participants on the Mediterranean diet, there were 17 fewer deaths for every 1,000 people over a five-year period, versus participants who stuck with their usual diets. Similarly, they suffered 17 fewer heart attacks and seven fewer strokes per 1,000 people.
The benefits were smaller in the low-fat trials, which had participants restrict their fat intake to 20% to 30% of daily calories. Over five years, people on those diets suffered nine fewer deaths and seven fewer heart attacks per 1,000, versus participants who made no diet changes.
Bradley Johnston, of Texas A&M University in College Station, led the analysis.
Both dietitians said the results highlight the benefits of Mediterranean-style eating. Gentile did note, though, that there can be too much of a good thing.
"The Mediterranean diet is also about moderation," she said.
Nuts, for example, are rich in nutrients, but also calories. A serving of nuts per day means a small handful, Gentile noted — not munching on half a canister.
The American Heart Association has advice on heart-healthy eating.
SOURCES: Connie Diekman, RD, MEd, food and nutrition consultant, St. Louis, and former president, Academy of Nutrition and Dietetics, Chicago; Theresa Gentile, MS, RDN, spokesperson, Academy of Nutrition and Dietetics, Chicago; BMJ, March 29, 2023, online