Diet quality is difficult to define. Traditional diets are considered high quality diets, yet they differ around the World and between populations. However, generally high quality diets are high in foods that have relatively lower energy densities such as whole grains, lean meats, fish, fresh vegetables and fruits. The relatively lower energy densities of high quality foods also by definition means that they are relatively higher in vitamin and mineral content per unit energy. Low quality diets are therefore those of higher energy densities such as those that contain refined grains, unnecessary and additional fat and sugar, with a relatively low concentration of vitamins and minerals per unit energy. Where fats are present in high quality diets they tend to be relatively higher in essential fatty acids and unmodified and unprocessed fats, compared to the saturated and processed and modified fats of low quality diets. Studies suggest that consumption of high quality diets may be related to socioeconomic factors in developed Western nations
Evidence in the literature suggests that energy dense foods may increase the likelihood of over consuming energy. This may seem obvious, but the idea is controversial and requires explantation. Healthy individuals possess intricate hormonal and neuronal signals that prevent overeating. When energy intake is sufficient, negative feedback is initiated and this reduces further energy intake. This system is highly effective and ‘hiding’ the true energy content of the food is not able to fool this system that can calculate the amount of energy consumed as well as that in storage, and can then come to a decision to curtail intake if energy requirements are met. However, this system is disrupted by the consumption of refined crystalline fructose, which induces insulin resistance in the individual. As insulin is a key hormonal signal in appetite regulation, once insulin resistance is initiated, the appetite regulatory mechanism fails, and the consumption of food is not able to trigger the curtailment of intake.
A low quality diet is a marker for sugar intake, and therefore fructose intake. Fructose is known to disrupt normal appetite regulatory mechanisms through the induction of insulin resistance. Low quality diets tend to contain high energy foods, but these alone are not enough to cause obesity, it is the presence of sugar, or specifically fructose that allows this to occur. The Eskimos have high energy diets as they eat seafood that contain high amounts of fat. The Maasai too eat high fat foods including milk and animal flesh as the mainstay of their diet. However, they do not overeat as they do not consume sugar and therefore they do not develop insulin resistance. High energy foods alone are therefore not enough to cause obesity, they must contain fructose, which is the catalyst that triggers the ability of the high energy foods to cause weight gain. High quality diets tend to contain less processed foods and also contain less sugar and so are less likely to cause weight gain compared to lower quality diets.
However, high quality unprocessed foods are more expensive than lower quality processed foods in the West. In addition, the poor often have access to only lower quality foods, or do not have the nutritional knowledge to make informed decisions about diet. Socioeconomic status therefore dictates eating habits and this in turn dictates disease rates. Exceptions exist, but it cannot be denied that fast food and low quality food is becoming increasingly cheap in the West and this attracts those with the lowest incomes, while the cost of high quality food continues to rise, excluding the same group. The promotion of high cost foods based on findings from nutritional research to low income families as a solution to health is unlikely to be successful because ignoring the cost of the food detaches the recommendation from reality. Taking into account the fact that some families have access to limited resources must be a consideration in all nutritional recommendations if the health of the individual is to be improved through diet.
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