Cereal for breakfast. A turkey sandwich for lunch. Chicken for dinner. If this sounds like your daily menu, it's time to shake things up.

"Just as your lifestyle changes in each decade, so do your nutritional needs," says Melina B. Jampolis, M.D., an internist and author of "The Busy Person's Guide to Permanent Weight Loss." "For example, a twentysomething needs to take calcium and vitamin D for strong bones, while a woman in her 40s should eat plenty of lean protein to help maintain muscle mass."
Dig into the tips, tools and meal plans you need to stay slim, strong and healthy at every age.

YOUR 20s
The challenge: You're pressed for time.
"Women in their 20s are notoriously unhealthy eaters because they frequently consume the majority of their meals on the run," says Fitness advisory board member Madelyn Fernstrom, Ph.D., director of the University of Pittsburgh Weight Management Center.
Trouble is, the more you grab food on the go, the more fat you take in, research shows. Plus, a diet that's low in vitamins and nutrients now may eventually lead to serious health problems, like heart disease and osteoporosis.
Your diet to-do list
• Bone up on calcium and vitamin D. "This is the last decade in which you can build bone mass without bone loss, a process that begins in your 30s," Fernstrom says. Aim for 1,000 milligrams of calcium (one serving of dairy, such as a cup of yogurt or
1 1/2 ounces of cheese, provides roughly 300 to 400 mg) and up to 1,000 IU of vitamin D daily. Since it can be tough to get enough D from food alone, your best bet is a combination of foods, such as salmon and canned tuna in oil, and supplements. Look for a dual supplement made from easy-to-absorb calcium citrate and vitamin D3.
• Fish for happiness. Long hours at the office and a fully booked social calendar can result in chronic stress, which "can raise blood pressure, promote weight gain and cause mood swings," says Fitness magazine's advisory board member Mark A. Moyad, M.D., director of preventive and alternative medicine at the University of Michigan Medical Center. "Research shows that eating 500 to 1,000 milligrams of omega-3 fatty acids daily can lessen the damage."
These good-for-you fats, found in fish, nuts and seeds, reduce inflammation and improve the health of your brain cells, helping to elevate your mood and protect against depression.

YOUR 30s
The challenge: You're low on energy
Feel like you're being pulled in a zillion different directions? No wonder. Between a demanding career, a husband or significant other — maybe kids, too — and trying to fit in a workout whenever you can, it's tough to balance all the things on your to-do list and still muster the motivation to eat right. Consider this your health wake-up call: "A less-than-stellar diet starts to catch up with you in this decade, putting you at increased risk for high blood pressure, high cholesterol and weight gain," Fernstrom says.
Your diet to-do list
• Bolster your immunity. Antioxidants like vitamins A, C and E, found in foods like sweet potatoes, red peppers and almonds, may slow the effects of aging and ward off heart disease and cancer. They reduce inflammation and repair cell damage. You can't get the same benefits from supplements, however.
"Studies show that the antioxidants in food are much more effective than those you get from popping a pill, because they work in tandem with other compounds to fight disease," explains James Joseph, Ph.D., of the Jean Mayer USDA Human Nutrition Research Center on Aging in Boston.
• Power up your plate. Filling up on fruits, vegetables, legumes and whole grains may reduce your risk of diabetes, cancer and heart disease.

YOUR 40s
The challenge: You're fighting belly flab
Toning this trouble zone is harder now. "When you're younger and producing more estrogen, fat travels to your hips and thighs," explains Pamela Peeke, M.D., a Fitness advisory board member and author of "Body for Life for Women." "Once you reach your 40s, you produce less estrogen and fat goes straight to your belly instead."
Your diet to-do list
• Ignite your metabolism. "The more muscle you have, the more calories you'll burn on a daily basis," Peeke says. The key is protein: It fuels muscle growth and helps keep you full between meals, so you'll eat less. Aim for 60 to 80 grams a day from a mix of lean meats, beans, peanut butter and dairy.
People who ate three servings of dairy a day for six months lost two more pounds of belly fat than those who consumed a low-dairy diet, according to a study. Researchers say calcium may assist enzymes that break down fat cells in your body.
• Water down your appetite. In your 40s and beyond, you burn about 100 fewer calories a day. Eat plenty of low energy-dense foods, such as salads, vegetables, soups and nonfat yogurt.