General Nutrition
Food differs from medicine, only in the intensity of the delivery process. In the short-term most foods are harmless. Your body is well able to cope with over-eating, or over-drinking, if that happens occasionally. However, if we choose our diet badly, firstly, your body adapts and tries to compensate. When we continue that practice over many years, the body's effort to cope is likely to cause 
inflammation, and slowly that is likely to become a "lifestyle disease."
Because your diet is controlled by you, it gets very little attention. You can only successfully control your diet, if you yourself have good knowledge. Otherwise you live in blissful ignorance until something happens to your life to force you to take notice. You can significantly change your life by changing your diet. There is much to learn, so start slowly, but be sure to start. Don't put it off, the only learning that counts is the learning you do. 50 years of prejudice and misinformation, is not easy to overcome. Buying the nutrition book you didn't read, or visiting this web site and not following up with repeated visits, is a mistake you can avoid.
If you are going to learn about the chemistry of your food, and understand how it affects your body, you'll need to keep notes, and you'll need to experiment for yourself. There is a practical way to do this, making small changes, and building routines for planning meals, and eventually for changing your lifestyle.
You must not assume that dieticians and doctors are good authorities about your diet. So much has changed in the last 10 to 15 years, and because of that the tide of change seems to be running even faster.
Ancel Keys, almost single handed, created the basis for our current obesity epidemic. He was helped along by a political desire to build a strong market for American corn and wheat, and a failed politician's need to be seen to be doing something really "great" (Senator George McGovern, after his failed bid to be President), in this case, to reduce the rising level of heart disease in America.
Everybody KNEW, what a healthy diet was, and how to prevent heart disease. Or so we were told. Modern medicine would save us all. So here are some of the failed "solutions" for the last 50 years: President Eisenhower's Heart attack: The Framingham Heart Study: The Anti-Coronary Club: Multiple Risk Factor Intervention Trial: The Women's Health Initiative. That brings us up to 2006, and "the answer" seems to be, that we don't KNOW, at all.
That is a great step forward. When you don't know you can begin to look for what you've "lost". In fact, when you do that, many new possible solutions pop out of the woodwork. Like the Ketogenic Diet, abandoned by researchers in the late 1920's.
When you don't know the answer, real science can finally overcome political dogma and prejudice. Dr Vilhjalmur Stefansson, Dr George Mann, Dr Weston Price, Dr Fred Kummerow, Dr Robert Atkins, and more recently, Dr Stephen Phinney, battled for years against the prejudice that "we already know" the answer. They all tried to show that Ancel Keys was wrong. We live with that misdirection of nutrition "science" today.
A large number of people are still taking statins to reduce their LDL-Cholesterol. Why? The science says that the side effects are much worse than any possible benefit. Type 2 diabetes is increasing at epidemic levels. Why? With a good diet, the need for additional insulin can be reduced and often eliminated. Type II Diabetes can be reversed, not by medication, but by proper diet. Too many people are obese. Why? Getting your weight under control is possible if you are well informed. Later in life cancer and Alzheimer's disease threaten to disable many of us. New science seems to show that by diet, exercise and attention to your lifestyle, that Alzheimer's (Sometimes called type III diabetes.) can be avoided.
In the 1950's it was thought that the key to the rising rates cancers in modern community was in understanding genetic variation in our DNA. Many researchers have reported that in communities that eat what we would call a primitive diet cancer is virtually unknown. So perhaps some cancers at least like diabetes are metabolic diseases, as Prof. Thomas Seyfried has proposed, we should avoid a diet that feeds the growth of cancer cells.
Nutrition Science Undeveloped
Nutrition science was the focus of the home economics department in most universities. Physiology and organic chemistry were not part of the course.
Richard David Feinman, a biochemist, reports being shocked and the bad science and lack of science in standard nutritional textbooks, that were "far removed from serious science." Since 2000 he has been working hard to educate dieticians, and the medical profession, about biochemistry, and the many new studies that disprove much that is commonly said by "nutrition experts."
Feinman says, "If a study describes a diet as "healthy," it is almost guaranteed to be a flawed study. If we knew which diets were "healthy," we wouldn't have an obesity epidemic."
Richard Feinman, is one of the researchers leading the way in the reform of nutritional studies, making them science based, biochemistry and physiology based, rather than based on "good home economics", and good culinary skills, as was common in the past. Some of the new science is quite remarkable, but little known.
Metabolic Syndrome
Dr Gerald Reaven identified many years ago that six common health problems were not six different diseases at all; but six common problems with one cause.
The six "diseases are now called metabolic syndrome, which is really an acquired intolerance to carbohydrates. Too much sugar, and too many whole grains, and too many potatoes over a life time, causes the body to become resistant to the way you are feeding it. The solution is to change the way you are eating.
