Dietary advice is a mixture of fad diets, science, tradition and market driven commerce. Fortunately, Matthew Martin, middle class non-professional nutritionist is here to sort things out for everyone. Sit back and let me over simplify things for you.
Eating too many calories will make you fat. What “too many” means depends on how much you exercise. Now how do you need to modify your life style and diet so you don’t have an uncontrollable urge to eat too many calories? Jury is out on that one.
Eating too few calories will make you lose weight. This is usually not a problem, but studies of large populations show that taller heavier people do better than shorter skinnier people.
There is an optimal weight. Add the two facts above and we find out there is an optimal weight to height ratio, which works out to be a BMI in the low 20s.
Losing Weight. Diet will keep you from gaining weight further, but exercise is what gets rid of the excess weight you have now. Keep in mind that once weight is put on, it goes away slow, maybe 2 pound a week at best. Also, people tend to overestimate the impact of exercise–the human is a very fuel efficient machine.
The jury is out on the optimal mix of fat, protein and carbohydrates in the diet. If the life extension research is true for humans (as it is true for mice), then the mere act of eat any calorie tends to wear out the body. On the other hand, eating extremely low calorie life extending diets means your body switches to a low temperature, low activity metabolism that wouldn’t make life much fun.
The key finding in current macronutrient research is that the mix of macronutrients you eat affect the ‘mode of metabolism’ you body is in. It appears depending on the food we are eating, we switch to fat burning mode, fat accumulation mode, starvation mode, etc. The macronutrient mix also affects how powerful our desire to eat will be. Furthermore, the predominant macronutrient we eat will put different strains on different systems. Low fat diets stress out the pancreas, high fat diets stress out the arteries, high protein diets put stress on the kidneys. Something is going to break- no one know if we are better off wrecking our pancreas in the effort to live longer or if it is better to wreck our arteries to live longer.
Protein is extremely good if you are doing any activities that require it, such as being pregnant or weight lifting. Extremely high protein diets mean your body has to take extra steps to turn that excess protein into fuel. So there is an optimum amount of protein to eat.
Fats can be ordered from bad to very bad. This is not very useful advice, especially now that carbohydrates are getting a bad reputation. If we don’t eat fat, carbohydrates and only an optimal amount of protein, we don’t get enough calories. What gives? Well, at best the macronutrient research can tell us what types of fat and carbohydrates we should try to eliminate all together, and which we should disproportionately favor.
Dietary cholesterol is either bad or neutral, so on average animal fats aren’t helping any.
Saturated fats (those solid at room temperature) are bad, but not deadly bad. On the other hand transfats, fats that are made solid by bubbling hydrogen through them are poison.
Low saturated vegetable oils are not as bad as the other fats. That said, be less bad than the other doesn’t mean they are good, like I said, the jury is out on that.
Transfats are poison. ’nuff said. Don’t even eat trace amounts of transfats if you can help it.
Carbohydrates can be ordered from bad to very bad. Refine starch and sugars are bad. Whole grains are not as bad. Fructose and the other simple sugars are not as bad as sucrose, but being not as a bad as sucrose doesn’t mean it’s good. In fact, gratuitous simple sugars in the diet appear to be wrecking our pancreases.
Animals. Jury is out on the effect of eating animals, milk and eggs. Vegetarians typically do a better job of controlling weight, which is supposed to be good for preventing or deferring degenerative disease. Also, just like diets that target one macronutrient over another, a vegetarian diet has powerful incentives involved. Many vegetarians stick to their diet because they have strong political, environmental and ethical reasons for sticking to their diet. Compare this to a low fat or low carb diet, where there is no similar consequences to abandoning the diet.
Diverse Diet. Eating a little bit of everything is a good idea.
Vitamins. Not getting enough is catastrophic. Getting extra vitamins appears to be a wash–no dramatic benefit or harm. Consider vitamins to be an insurance policy against accidentally eating an undiversified diet.
Single factors. No single behavioral or nutrition factor explains health or lack of it. We know that dropping transfats and dietary cholesterol is good, but other factors– like how many well-patient visits you make to your doctor might out weight all those factors. Also, focusing on easy to measure single factors, like oat-bran, grams of carbohydrates will distract us from possibly more important things, like exercise, smoking, alcohol, risky behaviors and many other issues whose presence can swamp the effect of a single factor behavior like eating more oat bran.
Appropriate skepticism. Be skeptical of brand new claims. Back in the day when bleeding was the state of the art treatment for microbial diseases, people would have been better of with no medical care at all, but if people had rejected all medical care would have been worse off, as even medieval medicine sometimes helped!
We are in a new age where things are more complicated. The low fat and the low carb diets are probably both right and probably both wrong depending on how future research pans out. There is a correlation between certain components of fats, such as transfats and certain types of cholesterol and heart disease. Similarly, there is a correlation between carbs and diabetes. And both carbs and fats have calories which are correlated to weight which is correlated to diseases. Holding an idea as tentatively true and acting on it is difficult, but we have no other choice if we are to progress in a scientific manner.