THE HEALTH case against regularly eating red meat keeps getting stronger. At what point is the data convincing enough for Americans to change their diets? One recent study found that eating red meat increases the risk of type 2 diabetes; another paper finds a diet low in meat, sugar, and salt but rich in vegetables and legumes is associated with a lower risk of Alzheimer’s.

And both studies — which followed thousands of people for decades — show that replacing even a few servings of meat can have an impact.

There are also implications here for the legions of people expected to try the new class of obesity drugs called GLP-1s. While studies have shown the drugs can induce enough weight loss to improve cardiovascular and kidney health, a lower body mass index (BMI) doesn’t solve all ills. “Losing weight will not entirely prevent you from developing other chronic diseases. You still have to rely on a healthy diet,” says Xiao Gu, a postdoctoral fellow at the Harvard T.H. Chan School of Public Health.

Mr. Gu is one of the authors of the new study linking red meat to diabetes. His team found that people who routinely consume more than a serving per day of red meat have a 50% higher risk of developing type 2 diabetes than those who partake at lower levels.

More than a serving per day might sound like a lot. But as my Bloomberg Opinion colleague Mark Gongloff recently pointed out, Americans are among the world’s most voracious meat eaters, with each person consuming an average of 280 pounds per year, which amounts to about three servings a day.

That meat-heavy diet comes at a clear cost to our climate, as livestock farming is responsible for some 18% of global greenhouse gas emissions. And it is clearly bad for our hearts; the greater a person’s red meat consumption, the greater their risk of cardiovascular disease.

But the link to type 2 diabetes has been a subject of ongoing debate. Some research suggests various components of meat can impair insulin function, whether the culprit is saturated fat, the meat’s iron content, or something in how the meat is prepared — grilling, curing, and overcooking have all been associated with poorer health outcomes. However, causation has been hard to prove: One recent meta-analysis found the link between saturated fat in red meat and diabetes tenuous at best.

Diet’s impact on health is also notoriously hard to study. What we eat changes over time and is just one factor affecting our risk of developing a disease — our genes, environment and lifestyle matter, too, as do socioeconomic factors.

The Harvard team took special care to account for those confounders. They used data from the Nurses’ Health Studies, which have followed more than 200,000 health care professionals for more than 40 years. That meant enough cases of diabetes had accumulated — more than 20,000 — to find the association between meat consumption and diabetes. And because volunteers were interviewed every two to four years, researchers had good information about how participants’ diets changed over time; by contrast, many other studies have only looked at diet at the time a study began.

One of the biggest confounders they had to untangle was body mass index (BMI). If people who eat a lot of red meat eventually gain weight, it could be their weight — not the meat — that leads to insulin resistance. But the researchers found that BMI only accounts for about half of the increase in risk. That means that red meat increases diabetes risk even for people who aren’t overweight. And processed meat — like sausage and salami — increased diabetes risk the most.

If that isn’t enough to convince you to cut back on meat, consider another new study. This one, which mined data from the NYU Women’s Health Study, found that people who ate more red meats, sugar, and full-fat dairy had a higher risk of Alzheimer’s disease.

Between 1985 and 1991, researchers enlisted some 14,000 middle-aged women and followed up with them for decades. Using data from about 5,000 women in the cohort, they found that people adhering to the “DASH” diet (shorthand for Dietary Approaches to Stop Hypertension) had a 17% lower risk of developing two or more cognitive issues later in life. In other words, a heart-healthy diet favoring plant-based foods fared better than those who consumed more red meat, sodium, and sweets.

The NYU team’s findings suggest the dietary choices made in midlife have a far-reaching impact on women’s health, whether it protected (or harmed) their heart or their brain, says Yu Chen, a chronic disease epidemiologist at NYU Langone who led the study.

Both studies do have some limitations. The Harvard study’s dataset is predominantly White women; the NYU study was more diverse but measured cognitive challenges across a short time frame — more follow up would better capture changes in brain health.   

But the take-away from both studies is clear. Your health will be better if you swap some lentils for that steak. — Bloomberg