The old cliché "we are what we eat", really has a lot of truth to it. In terms of the elements of life over which one has most control, food is undoubtedly the primary instrument for maintaining and improving oone's health. Not only do all of the chemical building blocks of the body's tissue come from food, but so do the fuels that the body burns, the vitamins which catalyze many of the body's chemical reactions, and some of the toxins which can harm the body if not properly dealt with. In fact, the only chemicals that are needed for life and that are not contained sufficiently in food are the oxygen from the air that is inhaled and the water that is drunk.
This section presents the theory and practice of food consumption which current scientific evidence has convinced the authors is most conducive to a healthy, happy and long life. Since individual humans have enormous genetic variation that is additionally compounded by the alterations of development and the modifications wrought by external insults during a long life-time, as well as enormous variation in a life-time of acquired tastes in food, no one diet will be optimal for everyone. Allowance for that is made by suggesting alternatives, within reasonable bounds, which the authors think can still be very healthy.
The essence of healthy eating is to keep calories low while maximizing the ratio of nutrients to calories, ie. eat as little as possible of only nutrient-dense foods while still retaining quality of life (see Calorie Restriction). In the context of food, nutrient means any vitamin, mineral, fat, amino acid, or other chemical that is found within food and has been shown to promote health and/or longevity when consumed within certain dosage ranges in conjunction with other nutrients. Implicit in the recommendation to eat foods that are as nutrient dense as possible is the assumption that harmful dosages of such nutrients cannot be obtained from food sources the could be eaten as part of a diet not causing obesity. If only actual foods are included, there seems to be no exception to this assumption.
More recently, there has been accumulating evidence that the amount of calories eaten may be not the major factor behind the large amount of evidence showing that calorie restriction with adequate nutrition in all animal species extends maximum lifespan. Instead a more fundamental factor appears to be the amount of time that the body is in a fasted state, during which glycolysis does not occur and the hormetic effects of a continuous, but mild hunger stress can have its beneficial effects. In particular, this lack of glycolysis in the fasted state means that fats and proteins will be metabolized to supply the body's energy needs. This in turn can have the beneficial effects of elimination of excess fat by lipolysis (hydrolysis of fat) and/or accelerated recycling of body proteins by autophagic proteolysis, some of which proteins may be dysfunctional and for which elimination is effectively anti-aging. Therefore, it is now recommended that at most two meals daily should be eaten and if possible only one, in order to increase the total daily length of the fasted state. It is imperative that no snacks are consumed between meals, since that will terminate the fasting state and the benefits obtained from it.R1,R2,R3,R4,R5,R6 The protein recycling effects of the fasted state can be additionally enhanced by the use of a lipolysis inhibitor such as niacinR or the more potent niacin analogue acipimox to increase autophagy, although lipolysis inhibition may be counterproductive if one is attempting to eliminate body fat. Exhaustive exercise while in a fasted state, by eliminating glycogen reserves (a stored source of glucose), will also enhance autophagic proteolysis.
Except for the small amounts which may be necessary to meet the needs of the brain's glucose requirement, there is no evidence that the sugars, starches and other carbohydrates that can be used by the body for fuel are an essential part of dietary intake. Practically, however, almost all foods contain some fuel carbohydrates, as well as some fiber carbohydrates (which are nutritionally helpful if not truly essential), and any minimal carbohydrate requirement which exists is always met by a real food diet. In fact, the major thrust of the approach detailed here, is to minimize metabolizable carbohydrate intake in addition to minimizing calories and maximizing nutrient density. The major reason for this is that not only do metabolizable carbohydrates ultimately generate free radicals while generating ATP (as do other fuel molecules), but in addition they are metabolized by conversion to sugars (mainly glucose) which then spontaneously attach to body proteins (through a process called glycation, or non-enzymatic glycosylation). Glycation of proteins reduces their functionality, causes crosslinking within and between proteins (additionally reducing their functionality), decreases the turnover rate of damaged or unneeded proteins, and spontaneously continues biochemical modification to form advanced glycation end-products (AGEs) that harm the body in many ways, some quite well defined by now.R1,R2,R3 There is also mounting evidence that eating mostly carbohydrates with a low glycemic index (GI) will be additionally healthful by eliminating surges of blood glucose levels, which can overpower the glycation prevention mechanisms of the body.R1,R2 This is part of the reason why, except for occasional and very small quantities as taste treats, pure sugar, white potatoes, wheat breads/cereals, wheat pasta and many fruit (or carrot) juices, taken by themselves, should not be ingested.
Two general forms of polyunsaturated fatty acids cannot be manufactured by the human body and certain minimal amounts of fats have been found to be essential in the human diet. These two forms are denoted by the chemical family names omega-3 and omega-6. Any healthy human diet should contain a minimum of 5 grams of omega-3 and 15 grams of omega-6 daily. In addition, there is evidence that the ratio of omega-6 to omega-3 should be kept between 2:1 and 4:1 although this may vary depending on the exact types and amounts of these and other fats which are consumed.R1,R2,R3 While the human body can produce monounsaturated fatty acids (types omega-7 and omega-9), there is good evidence that additional dietary sources of these can be highly beneficial.R1,R2,R3 Therefore, it is also recommended that a healthy diet should contain a minimum of 15 grams daily of monounsaturated fat preferably from extra virgin olive oil, which studies show contains other beneficial nutrients.R1,R2,R3 Although some saturated fats (mainly stearic acid) appear to be neutral with respect to their effect on cholesterol and atherosclerosis,R1,R2 none of them are essential and, since unessential calories are should be minimized, saturated fats should be eaten as sparingly as possible except when they are contained with otherwise healthful foods and except for the shorter chained saturated fats (less than 12 carbons), which have shown some benefits.R1,R2 As with fuel carbohydrates, any varied and healthy diet will contain necessarily some saturated fats of all kinds.
Although the human body is fundamentally built from amino acids in as much as proteins (chains of amino acids) are the only chemicals directly produced by DNA, most of the protein in a healthy body is produced from the metabolism of old proteins (referred to as proteolysis, catabolism, turnover or recycling) into their constituent amino acids and the reuse of these amino acids. Thus, the daily requirement for fresh amino acids is really quite small relative to the total daily protein production of the body. Dietary amino acids are generally needed only to replace amino acids burned for fuel by gluconeogenesis, to restore the proper proportions of amino acids necessary for the current protein building, to generate new tissue, and as the raw material to produce neurotransmitters and other non-protein but essential body chemicals. Since these are all such important functions, a recommended daily amount of dietary protein (as a source of amino acids) is 1 gram per pound of lean body mass. In addition, the proportions of amino acids in the protein should as much as possible match the needs of the body for fresh amino acids, which needs depend somewhat on what the body has been doing and requires them for.
In an effort to further understand the essentials of the longevity effect of calorie restriction, protein and individual amino acid restriction experiments have produced accumlating evidence that methionine restriction alone can have essentially the same benefits as calorie restrictionPMID: 19414512, PMID: 18682147 and may be easier to achieve because of its production of less hunger.PMID: 18252204 A table has been created by the authors to help them restrict methionine.