Eating the right kind of nutrients, proportions and quantities is all that it is about, quality, quantity and variety. A really good diet is summarized in a few words: A high fiber, low carbohydrates, low-fat and low-salt but ample amount of protein, vitamin-D, and rich omega fatty acids ( omega 3 ). Another aspect to this is “natural foodâ€. Avoid artificial flavors, coloring, MSG, artificial sweeteners, Pesticide, hormone, antibiotics and bone meal contaminated foods. A simple way of putting it: if you can grow it then you can eat it.
High fiber diet
Vegetables and whole wheat and other grain and nuts are high in fiber. Fruits have more calories than vegetables due to fructose. Every calorie counts when one is trying to lose weight. High fiber diet helps you regulate your blood sugar and your colon function in preventing constipation, irritable bowel syndrome and the resulting diverticulosis.
Low carbohydrates
Carbohydrates are considered inflammatory food.  They cause insulin reaction which in turn causes one to ingest more carbohydrates in a vicious cycle leading to obesity and diabetes.  Carbohydrates cause a person to feel sleepy and sluggish after a meal.   Excess carbohydrates cause acceleration of atherosclerosis and higher incidence of strokes and heart attacks.
If you are trying to lose weight, then low carbohydrate is the way to go. The trend of your weight and whether it goes up, down and remains stable, is a function of the number of calories in versus the number of calories out.  It is just like your bank account. Low carbohydrates diet, means to curb your intake of wheat, rice, potatoes, corn and sugar products. Examples: Bread, pasta, lasagna, cakes, cookies, muffins, crackers, pretzels, fries, honey, corn syrup products such as soft drinks, pancake syrup and cane sugar.
Low fat
Avoid animal derived fats; fatty meats, sausage, bacon, cold cuts, luncheon meats and butter. Avoid trans fatty acids. Incorporate the good fats in your diet that come from Avocado and peanuts. Small amounts of olive oil, canola oil and a daily dose of fish oil is also appropriate.
Adequate protein
When discussing a good diet, words like: “eat a lot of†really should be used sparingly. Eating healthy is in large part about portion control or rather, eating the right portions. When it comes to eating protein, fish, chicken or turkey is preferable over red meat. The size should fit in the palm of the hand. Quarter the dish should come from lean meat, Another quarter from high fiber carbohydrate source and the other half should come from vegan source.
Quantity vs. quality
A person can gain or lose weight if eating quality food. It all depends on quantity, The number of calories in versus the number of calories out. Calories can come from low quality food or from high quality food. In other words; the concept of quantity is used to steer the weight up or down and the concept of quality is used as a health measure: Examples of this are the use of lower glycemic index foods to dampen the insulin response. Another example is the use of antioxidants to mitigate and neutralize inflammation in the body that results from free radicals, stress and wear and tear.
Low salt
Salt helps absorb the sugar. Eating salt makes you want to eat carbohydrates and vice versa. Humans are born with kidneys that filter at 100% capacity in early years. This number goes down 1% per annum.
At age 50, roughly a significant percentage of kidney function has been consumed. The kidneys no longer filter the salt as it used to in early years. Salt tends to accumulate and hypertension ensues.
Salt is a potent factor in raising the blood pressure, therefore, avoiding salt is also a powerful measure in treating hypertension. From my practice over more than 20 years, salt restrictions always worked in reducing the blood pressure, though by itself, it may not be an adequate measure in treating hypertension.