I believe that a healthy diet is one which maximizes nutrients and minimizes toxins.
So we have made a few assumptions here.
1) We eat food for the nutrients in it.
We have a more or less fixed need for body building nutrients, based on body composition. The variation is mostly due to various health factors. While the need for energy giving nutrients varies wildly based on activity levels. Excess of some nutrients can be harmful, this depends on the ability of the body to excrete them.
2) Foods can also contain toxins in them.
Small amounts of toxins can be good, via hormesis. The healthy limits are small for toxins. The toxins can be neutralized by the body (liver), but there are strict limits to them.
It is important to determine bioavailability of nutrients before saying that a particular food group has nutrients. And we should always compare density of nutrients with energy in the food. There is no point comparing 100gms of wheat with 100gms of spinach, because you will get very little energy from spinach, so you can eat a lot of it without overeating. Although there are other constraints like fiber, and excess of nutrients.
It is also important to understand that almost all toxins are proteins. Proteins are what our body reacts against. The whole immune system is geared against those. Non-protein toxins can be very bad because the body will not know how to react to them.
What is very low in toxins? It is animal meat. Why? Ever tried to give aspirin to a cat. These are obligate carnivores, and do not have the genes to process toxins. Why did they evolve like that? Because they eat only meat, and have no need to process toxins. If you find a cat that eats plant material, you will find that it is domesticated and that it is sick. This does not say that animals cannot produce toxins, some do to use as offensive weapons. The toxin is harmful to the animal itself and so is contained in a well protected gland.
The belief that saturated fat and cholesterol is harmful is a belief that is rested upon the belief that mother nature is crazy. That it would actively store a harmful ingredient for future use. Most of the body stores of fat are saturated(SFA) and mono-unsaturated(MUFA). There is enough fat to last a few months, if there is no other calorie intake. Contrast it to the body's store of Glycogen (glucose + water). It lasts only more than a day, when a lot of energy use is obtained from fat. Why did body store SFA and MUFA instead of Glucose? The reason is that SFA and MUFA are very stable, they do not react easily and hence can be stored safely, while Glucose is highly reactive. So much so that glucose is not stored as glucose, but as glycogen. The other equally important reason is that the energy density of SFA and MUFA is quite a bit higher than glucose. In fact twice more than glucose, if glucose was not stored with water. Glycogen is not anywhere comparable. The body only stores longer chains (>16), because they are more stable and more energy dense, the lower chains are converted to ketones and used immediately.
If you find a research that shows that saturated fat is bad, you will find that the study is observational, where the people eating saturated fat also indulged in several unhealthy practices like smoking, eating manufactured, heavily processed food, abusing alcohol, no exercise, etc. You may also find that the researcher treated saturated fat and trans fat (a very harmful unsaturated fat) interchangeably, or that the research says something else while the abstract and summary says something else. There are so many ways to lie in nutritional research, for getting the almighty grants.
Fat is required to process fat soluble vitamins, E, A, D, K. What remains is B and C, and we think fats are useless. Check out what happens to people with gastric bypass surgery. They exchange their obesity with multiple fat soluble vitamin deficiencies. Of these only E comes from plant sources. Others are obtained from animal sources. D can be made internally from the sun. A and K can be made internally from plant sources. Some people cannot make sufficient Vitamin A, and most people cannot make sufficient vitamin K2. I am sure many doctors would not have heard of Vitamin K2, such is the state of medical science. There is a reason why Milk needs to be fortified these days, because the fat has been removed which contained those vitamins. Low fat milk needs to be enriched, but in the absence of fat, useless water soluble plant forms are put in it, just to claim that it is more healthy.
Many doctors do not know that Vitamin K2 is crucial to proper calcium utilization, in strengthening of bones and teeth. Have you heard very old people say that they have strong bones because they ate a lot of ghee in their childhood. Do you know the food that is very high in Vitamin K2? It is ghee from a grass fed cow. Only Natto and Aged Cheeses have higher K2 concentration. That generation is already gone. If you did hear it you would have heard it twenty years ago, when some of them were alive, after living 90 years. Since the last 50 years we have been eating manufactured oils. First it was hydrogenated fats, now they are refined oils. And we think that we are doing something healthy :-).
This does not mean that we should eat a lot of fat by itself, as it is also mostly empty calories. But foods that contain fat, also contain nutrients that are delivered by the fat content. Removing their fat makes them less complete, and harmful.
Cholesterol is created by the liver for several purposes, including immunity, upkeep of arteries, shuttling nutrients. There is no such thing as a bad cholesterol, only healthy or unhealthy cholesterol. A healthy LDL is not a bad cholesterol. An unhealthy cholesterol is bad, doesn't matter whether it is LDL or HDL. Why does it become unhealthy? Does diet have anything to do with it? Does oxidization of cholesterol has anything to do with it. Cholesterol are lipoproteins ie compounds of fats and proteins. So what kind of fat gets oxidized faster. Is saturated fat more easily oxidized or poly unsaturated fats? That is a basic chemistry question and anybody with a Pre-College level Chemistry should be able to answer this. Vit D is all the rage these days, but how does the body produce it without cholesterol. What are all the hormones made up of if not cholesterol. What about Neurons and Brain, much of it is Saturated fat and cholesterol, yes Omega3's also feature strongly.
OK enough about meat/saturated fat/cholesterol.
Lets talk about vegetables and fruits. We have already established that they have toxins. Does it mean we should not eat them? No, we are omnivores, this means that our body and the liver is able to handle toxins. Actually it is important to exercise the ability to handle toxins. It is like exercise. The exercise causes stress to the system, which forces the system to adapt, leading to a better health state. Similarly eating the optimum amount of toxins is healthy for us. There will be a J curve here, with less causing problems and an excess also causing problems. So the toxins within limits are not a problem. Vegetables and fruits also provide us with micro-nutrients that are very difficult to get from animal foods. This is why it is very important to eat them. Fiber is also one of the nutrients.
It is a myth that all kinds of fiber or a lot of fiber is good for us. Fiber provides food to the gut flora, which produce B and K vitamins and short chain fatty acids. The Short Chain Fatty Acids (SCFA) are very important for the gut health. What kind of fiber will be acted upon faster? The soluble type, and that is the type which is more healthy for us. Insoluble fiber is known to damage the gut lining, instead of helping it. Indeed vegetables and fruits are very rich in soluble fiber. Also fiber binds nutrients, so it is important to completely digest them, to get at those nutrients. There is a limit to how much gut flora our intestines can accept, and consequently how much fiber we can digest. We are not apes or cows.
Now lets get to the last type of food, grains and legumes. What kind of nutrients do we get from whole grains that we don't get from meat and vegetables/fruits? None, no such nutrient exists. If anybody can think of something please tell me. Are grains more rich in nutrients than meat and vegetables/fruits? Please compare them and get back to me if you find any grain which is more nutritious. Please do check the bio-availability of nutrients in grains, they are pathetic. Read about the discovery of vitamins, and how they were cured. They were all caused by deficiencies due to not eating meat, vegetables and fruits. They were never caused because of not eating grains or legumes.
The current belief in the healthiness of whole grain or rather whole wheat was manufactured by the USDA, whose mandate is to sell agriculture products. Nobody noticed the conflict of interest when they assigned them the task of defining the nutritional policy. Remember whole grains has only been compared with refined grains never with the absence of grains.
Yes, we can also improve the bio-availability of nutrients in grains and reducing the toxins in grains by processing them in certain ways. Soaking, grinding, filtering, fermenting, and cooking. Anybody remember how grains were handled in traditional times. We used to get our wheat, wash them in the water, dry it, then get it ground. Before making the dough we used to use a sieve to filter the bigger parts and cook the dough. We did not do the whole process that Europeans did because wheat has not been in widespread use in India for a very long time. Europeans additionally ferment it with yeast. South Indians do the same process to most of their grains and eat dosas/idly's made of these things.
Cooking is used to increase the bio-availability of nutrients in all kinds of foods. It is not just for the taste and texture. Fermentation is the second most useful processing technique for increasing bio-availability.
In older days people did not eat new foods everyday. They had very few staples and ate them day in and day out. The food was more related to what grew locally and changed seasonally. We do not need to eat a lot of variety everyday. Its actually better to eat same food everyday, because it keeps the food reward low, and prevents over eating. Varying food seasonally provides the variety without increasing food reward, and overeating. The body holds nutrient stores, which last typically around a year. Some critical nutrients like B12 are held for even 40 years. Some nutrients must be replenished on a daily basis, some of these are B vitamins, Vit C, and electrolytes. Vit C requires that we eat fresh raw fruits and vegetables. B Vitamins require that we keep out gut bacteria healthy, which requires eating pro-biotics and pre-biotics, fermented foods help here. Electrolytes and other minerals are best absorbed from cooked foods, which breaks down cell walls releasing Potassium and other intra cellular minerals. Boiling is probably the best way of cooking food. It is important to have raw, cooked, and fermented foods everyday. That is probably the reason for the ubiquity of pickles in all traditional cultures.
Richard Feynman once gave a lecture on the question "What is Science?". He defined science as follows
Science is the belief in the ignorance of experts.
So I have a question to the people brave enough to wade through all of this. Are you ready to question the ignorance of your nutritionists? This is how science works and your health depends on questioning this absurd status quo.
1) Avoid manufactured fats, and instead consume natural ones (Ghee/Coconut oil/Olive Oil/Mustard Oil).
2) Removing natural fats from foods is harmful.
3) Eat meat, it is good for you. Avoid meat from factory farms (mostly chicken).
4) Eat Vegetables and fruits, they are good for you. Avoid vegetables that give you problems of gas. You may not be digesting its fiber or toxins well.
5) Keep the consumption of grains/legumes low. Do not depend on them for nutrients. Process them well to make them more nutritious, and reduce their toxins.
6) Cooking is important.
7) Raw foods are important.
8) Fermented foods are also important, the ones with live bacteria, not the ones with Vinegar.