In his book In Defense of Food, Michael Pollan offers three simple, easy-to-remember “rules” for eating:
These guidelines are very aligned with the 2015 USDA recommendations  and those developed by Harvard’s Healthy Eating Plate , which include choosing whole grains, eating lean protein like fish and chicken instead of red meat, drinking plenty of water, using healthy oils, and filling almost half your plate with healthy produce.
Below are some general guidelines that apply to everyone and are important for good health.
Because there is such strong evidence linking obesity to many chronic or acute diseases, the World Health Organization and the U.S. Department of Health and Human Services recommend that you aim for a healthy body weight with a body mass index (BMI) between 18.5 and 25. BMI indicates an individual's weight status in relation to height, and it helps give a sense of a healthy ratio between the two. It doesn't apply to children, the elderly, or the very athletic.
Calculate your BMI with this tool from the National Heart, Lung, and Blood Institute .
Studies show that diet alone is not as effective in achieving a healthy body weight as diet combined with exercise. Physical activity has many other health benefits as well. See the Fitness and Exercise section  for recommendations on how to be physically active each day. Even relatively small weight loss can make a difference in health by reducing blood pressure and improving glucose tolerance and blood lipids.
Whether you are working to lose or maintain weight, you should make healthy food choices following the Dietary Guidelines for Americans , developed by the U.S. Department of Health and Human Services and the U.S. Department of Agriculture. These guidelines will improve your health, help you meet your nutrient requirements, and reduce your risk of chronic disease.
The dietary guidelines recommend that you get the most nutrition out of the calories you eat. There IS a helpful number of calories for you to use to gauge your food choices each day. Calculate your calorie needs .
To simplify healthy eating, the U.S. Department of Agriculture has replaced the traditional food pyramid with the Choose My Plate  graphic. We recommend the Harvard School of Public Health version, called the Healthy Eating Plate, which points consumers to the healthiest choices in the major food groups based on the best scientific evidence.
See also our Food as Medicine  topic for more specific information on what foods you should eat.
It is a common recommendation to drink 8 to 10 glasses of water a day to help your body's biological processes, especially carrying nutrients to cells and eliminating wastes.
The Institute of Medicine (IOM) advises men to consume roughly 3.7 liters (about 16 cups) of water a day and women to consume 2.7 liters (about 12 cups) of water a day. Eighty percent of this should come from drinking water and other beverages, (but not soda, coffee, or alcohol). The remaining 20% should come from foods—especially fruits and vegetables, which are 70% to 95% water.
Your water needs depend on many factors, including your health, how active you are, and where you live. It's generally not a good idea to use thirst alone as a guide for when to drink. By the time you become thirsty, you may already be slightly dehydrated. It is especially important for older adults to drink water before becoming thirsty, because your thirst sense is diminished as you get older.
How, when, and where do you eat? If you're like many Americans, you may often eat meals while doing something else: driving, talking on the phone, watching television, or reading. In short, you may pay little attention to your food. As a result:
Learn about why being mindful while eating matters .
In Salt Sugar Fat: How the Food Giants Hooked Us, reporter Michael Moss describes how executives at large food corporations have figured out the science of getting people to buy more of their products. In short, many processed foods are not designed to enhance wellbeing, but to exploit natural cravings for salt, sugar, and fat—and when coupled with colorful, attractive advertising, many unhealthy foods such as colas and sugary cereals become irresistible staples in the American diet.
The grocery store is a good place to practice mindful shopping. Check the ingredients label—many companies have begun to shovel harmful amounts of sugar and salt into foods you wouldn’t naturally suspect, such as spaghetti sauce, granola bars, and yogurt. Make purchase decisions based on USDA dietary guidelines: buy “whole foods,” such as fruits and vegetables, and skip processed foods, no matter how tempting and flashy their packaging may be. This is especially important if you have children, as much of the food giants’ marketing is aimed at exploiting the vulnerable willpower of young people.
Apart from the biological effects of eating on the run, there are social, psychological, and spiritual effects. Fast-food habits can deny you the benefits gained from preparing foods with mindfulness, appreciation, and care, and eating with others in a relaxing atmosphere.
Research demonstrates that the social component to eating is critically important to health outcomes and wellbeing. A 2011 study showed that children and adolescents who eat meals with their family 3 or more times each week increase their likelihood of developing healthy eating habits and maintaining a normal weight. Another study by a team at the University of Minnesota found that family mealtimes also decreased risk for substance abuse, sexual intercourse, depression, eating disorders, and poor academic performance among adolescents. It stands to reason that eating with others you care about is beneficial to everyone.