Think about this: If you're around 40, by the time you and nine of your friends hit age 70, chances are only one of you will be disease-free and have good physical, mental, and cognitive health. Yikes.

The good news is that you — and your friends — have a chance to change that, according to researchers at Harvard's T.H. Chan School of Public Health.

They looked at 30 years of data on more than 100,000 people and found that those who ate a healthy diet from age 40 onward were up to 84% more likely to be in great shape physically and mentally when they hit 70.

The healthy eating patterns that boosted future well-being included getting lots of nuts, legumes, and low-fat dairy, as well as fruits, vegetables, whole grains, and healthy fats.

Conversely, people who ate a lot of trans fat, sodium, total meats, and red and processed meats sabotaged their chance to experience healthy aging.

But don't wait until you're in your 40s to clean up your nutritional act. Another new study out of Tufts University that followed 3,000 people from age 4 to 70 shows that poor nutritional habits started in childhood have a major impact on brain function as you age.

In fact, the researchers found that only 8% of people who had a lifetime of poor nutrition were able to maintain high cognitive function as seniors.