Joy Bauer, a nutritionist and the author of “From Junk Food to Joy Food”:

What you put on your plate when you’re in your 20s and 30s can help set the stage for what happens tomorrow in a big way. For instance, here’s one minor tweak that will have significant payoff: Go meatless one to two days each week. Not only is it one way to help protect our environment by reducing our carbon footprint, eating less beef, pork and poultry (and in its place, more plant-based foods) often means better health, in the way of a lower body mass index, improved cholesterol, lower blood pressure and a decreased disease risk.

Joy Bauer is a nutritionist and author of “From Junk Food to Joy Food.” (Lucy Schaeffer)

[Weeknight vegetarian? Great recipes for going meatless]

Andrew Weil, a physician and the director of the Arizona Center for Integrative Medicine at the University of Arizona, and author of “Mind Over Meds”:

We naturally lose bone density and muscle mass as we age, which increases the risk of fractures, weakness, aches and pains, and limitation of mobility. How can you slow it down? Strength training with weights and weight-bearing exercise like running, walking and cycling develop the muscles and bones you need in later life.

Also, take 2,000 IU of vitamin D daily, and be sure your diet includes calcium-rich foods like dairy products, leafy greens and sesame.

Kenneth Lin, a family medicine physician and an associate professor at Georgetown University School of Medicine:

Many sexually transmitted diseases do not cause symptoms, but infections can damage fertility and be passed on to sexual partners. One common denominator for healthy young men is that they are having sex, so testing for HIV, gonorrhea, chlamydia and syphilis would be my highest priority for them. Testing is especially important for women younger than 25 (who have the highest rates of gonorrhea and chlamydia), but my top priority for young women would be screening for cervical cancer (typically, a Pap smear) every three years starting at 21. You may want to add HPV screening at 30.

[What men should know about cancer that spreads thrugh oral sex]

Richard A. Friedman, a professor of clinical psychiatry at Weill Cornell Medical College in New York:

The early adult years are the peak age for the onset of many psychiatric problems, including anxiety and depression, so catching problems early not only will ensure a faster recovery, it also could change the entire trajectory of one’s life. Young people also feel invincible, making them more likely to engage in risky behavior — unprotected sex, excessive recreational drug use, biking wihout a helmet — that could jeopardize the quality and length of their lives. Be aware of these impulses and try to moderate them.

Gunnar Peterson, a Los Angeles-based personal trainer:

Make a fitness plan, and stick to it: Lock in a routine that incorporates strength and cardio. The important thing is having a plan, and the more precise it is, the easier it is to follow. Schedule it the way you would a job interview or a business trip. Be open to spur-of-the-moment opportunities — they put the life in living — but then get back to your plan.