By Bonnie Liebman “Plant sources of protein look the best,” says Walter Willett, who chairs the Department of Nutrition at the Harvard T.H. Chan School of Public Health in Boston. “That includes nuts and beans, and even whole grains contribute some protein. Their fat profile is better than red meat’s, they have no cholesterol or heme iron, and they have essential nutrients and fiber. Red meat has no fiber. So when we put all of those things together, it’s not surprising that plant proteins are a healthier package.”
What’s best after plant sources?
“Poultry and fish,” Willett says. “Fish has a special contribution of omega-3 fats, which are sparse in some people’s diets. And poultry has better fats than red meats, so it’s not surprising that it looks better. And eating poultry hasn’t been linked to a higher risk of cancer, heart attack, stroke, or diabetes.”
What about dairy?
“It quite consistently looks better than red meat, but not as good as plant protein and usually not quite as good as poultry and fish,” he explains. “The dairy food that looks healthiest is yogurt, possibly because of its effect on the microbes in the gut.”
Why are plant proteins better for the planet?
“Red meat has the worst environmental impact of pretty much any food,” according to Willett. “That’s largely because cattle produce methane, a potent greenhouse gas. And they’re producing methane for long periods. The time to market is about a year and a half for grain-fed cattle and up to four years for grass-fed beef. In contrast, chicken comes to market in six weeks. So chickens are alive for much less time, and they don’t produce as much methane as cattle do.”
Why is red meat the least healthy source of protein?
“If you compare red meat to alternative protein sources, like poultry, fish, nuts, beans, or low-fat dairy, red meat is consistently linked to a higher risk of mortality or cardiovascular disease or diabetes, Willett explains.
“Part of it is the relatively high levels of saturated fat in red meat. Alternative protein sources have more unsaturated fat, and polyunsaturated fats in particular. Even poultry has more polyunsaturated fat than beef.”
There’s also recent evidence that the choline and carnitine in red meat are metabolized in the blood and in the GI tract to TMAO, which appears to cause a buildup of plaque in arteries, Willett says. And the cholesterol and heme iron in red meat are probably also factors.
What’s harmful about heme iron?
“Heme iron is the iron in meat and poultry that’s often been held up as a virtue by nutritionists because it’s better absorbed than non-heme iron,” Willett says. “But if we already have enough iron in our bodies, like 80 or 90 percent of Americans do, we continue to absorb heme iron whether we need it or not. And that could be harmful. Iron is a pro- oxidant that can damage cells throughout the body if you have too much. Too much heme iron, for example, increases the risk of diabetes.”
In contrast, the absorption of non-heme iron—which we get from vegetables, beans, nuts, whole grains, or supplements—is quite regulated. If we’re short on iron, we absorb non-heme iron well. But if we have adequate stores, then we essentially shut down our absorption. And that’s good.
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