The Harvard School of Public Health has recently published these great summaries on our food groups and their importance to our health.  For more detailed information go to their website:
http://www.hsph.harvard.edu/nutritionsource/what-should-you-eat/carbohydrates/index.html

Carbohydrates - Choose good carbs, not no carbs. Whole grains are your best bet.
Don't be misled by fad diets that make blanket pronouncements on the dangers of carbohydrates. They provide the body with fuel it needs for physical activity and for proper organ function, and they are an important part of a healthy diet. But some kinds of carbohydrates are far better than others.

The best sources of carbohydrates—whole grains, vegetables, fruits and beans—promote good health by delivering vitamins, minerals, fiber, and a host of important phytonutrients. Easily digested carbohydrates from white bread, white rice, pastries, sugared sodas, and other highly processed foods may contribute to weight gain, interfere with weight loss, and promote diabetes and heart disease.

Protein - Pay attention to the protein package. Fish, poultry, and beans are your best bets.
Animal protein and vegetable protein probably have the same effects on health. It's the protein package that's likely to make a difference. A 6-ounce broiled porterhouse steak is a great source of protein—38 grams worth. But it also delivers 44 grams of fat, 16 of them saturated. That's almost three-fourths of the recommended daily intake for saturated fat. The same amount of salmon gives you 34 grams of protein and 18 grams of fat, 4 of them saturated. A cup of cooked lentils has 18 grams of protein, but under 1 gram of fat.

So when choosing protein-rich foods, pay attention to what comes along with the protein. Vegetable sources of protein, such as beans, nuts, and whole grains, are excellent choices, and they offer healthy fiber, vitamins and minerals. The best animal protein choices are fish and poultry. If you are partial to red meat, stick with the leanest cuts, choose moderate portion sizes, and make it only an occasional part of your diet.

Fats - Choose healthy fats, limit saturated fat, and avoid trans fat.
The total amount of fat you eat, whether high or low, isn't really linked with disease. What really matters is the type of fat you eat.

The "bad" fats—saturated and trans fats—increase the risk for certain diseases. The "good" fats—monounsaturated and polyunsaturated fats—lower disease risk. The key to a healthy diet is to substitute good fats for bad fats—and to avoid trans fats.

Although it is still important to limit the amount of cholesterol you eat, especially if you have diabetes, dietary cholesterol isn't nearly the villain it's been portrayed to be. Cholesterol in the bloodstream is what's most important. And the biggest influence on blood cholesterol level is the mix of fats in your diet—not the amount of cholesterol you eat from food.

Fibre - Choose a fibre-filled diet, rich in whole grains, vegetables, and fruits.
Confused by fibre? Well, you're not alone. Most people are. But you don't have to know all the ins and outs of fibre to get benefit from it. When you eat a healthy diet rich in whole grains, vegetables, and fruits, you usually get most of the fibre you'll need, which means you'll also be lowering your risk of diabetes, heart disease, diverticulitis, and constipation. Not a bad package deal.

Officially, fibre is a type of carbohydrate that the body can't digest. Most adult women should shoot for over 20 grams of fiber a day; men should shoot for over 30 grams. Great sources are whole fruits and vegetables, whole grain breads and breakfast cereals, and all manner of beans.

Fruit & vegetables - Choose more vegetables and fruits. Go for color and variety—dark green, yellow, orange, and red.
It's hard to argue with the health benefits of a diet rich in vegetables and fruits: Lower blood pressure; reduced risk of heart disease, stroke, and probably some cancers; lower risk of eye and digestive problems; and a mellowing effect on blood sugar that can help keep appetite in check.  

Most people should aim for at least nine servings (at least 4½ cups) of vegetables and fruits a day, and potatoes don't count. Go for a variety of kinds and colors of produce, to give your body the mix of nutrients it needs. Best bets? Dark leafy greens, cooked tomatoes, and anything that's a rich yellow, orange, or red color.

Calcium and milk - Calcium is important. But milk isn’t the only, or even best, source.
It’s not a news flash that calcium is key for healthy bones. Getting enough calcium from childhood through adulthood helps build bones up and then helps slow the loss of bone as we age. It’s not clear, though, that we need as much calcium as is generally recommended, and it’s also not clear that dairy products are really the best source of calcium for most people.

While calcium and dairy can lower the risk of osteoporosis and colon cancer, high intake can increase the risk of prostate cancer and possibly ovarian cancer.

Plus, dairy products can be high in saturated fat as well as retinol (vitamin A), which at high levels can paradoxically weaken bones.

Good, non-dairy sources of calcium include collards, bok choy, fortified soy milk, baked beans, and supplements.

Alcohol - Moderate drinking can be healthy—but not for everyone. You must weigh the benefits and risks.
Alcohol's link with health is a bit Dr. Jekyll and a bit Mr. Hyde. Exactly which face it shows depends largely on who's drinking and how much. For most moderate drinkers, alcohol has overall health benefits. While moderate drinking can increase the risk of colon and breast cancer, these risks are trumped by the boost in cardiovascular health—especially in middle age, when heart disease begins to account for an increasingly large share of disease and deaths.

Non-drinkers, however, shouldn't feel the need to start drinking to improve their health. Heavy drinkers, with their increased risk of cancer, heart disease, high blood pressure, cirrhosis, and dependence should cut back or stop drinking altogether. A pregnant woman should also avoid alcohol, since it can cause brain damage to the unborn child.

What's considered moderate drinking? For women, it's up to one drink per day; for men, it's up to two drinks per day. What's considered a drink? A general guideline is 12 ounces of beer, 5 ounces of wine, or 1½ ounces of hard liquor, such as vodka or whiskey.

Vitamins -A daily multivitamin is a great nutrition insurance policy. Some extra vitamin D may add an extra health boost.
Trying to follow all the studies on vitamins and health can make your head swirl. But, when it’s all boiled down, the take–home message is actually pretty simple: A daily multivitamin, and maybe an extra vitamin D supplement, is a great way to make sure you’re getting all the nutrients you need to be healthy. The folic acid in most multivitamins helps prevent neural tube defects in newborns; it may lower the risk of heart disease, colon cancer, and breast cancer. Vitamin D from a multivitamin or single supplement can lower the risk of colon and possibly many other cancers.

Of course, there can be too much of a good thing. It’s important not to go overboard with vitamins. While a multivitamin and a vitamin D supplement can help fill some of the gaps in a less than optimal diet, too much can be harmful. In general, stick close to standard recommended doses in a multivitamin. And since your multivitamin will likely contain all the folic acid you'll need, stay away from cereals, protein bars, and other foods that are super-fortified with folic acid. 

Reference – Harvard School of Public Health, Boston
http://www.hsph.harvard.edu/nutritionsource/what-should-you-eat/carbohydrates/index.html