UCLA Center for Human Nutrition

Nutrition 101
Aspects of Human Nutrition

Human Nutrition comprises a wide variety of disciplines and requires the integration of a number of different conceptual models for research and clinical purposes. Nutrition begins with food choices, which are determined by availability as well as individual and social factors. These whole foods are the expression of eating behaviors, but they can also be analyzed in terms of their provision of macronutrients, micronutrients, and fiber. Nutrition can be further reduced to considerations of carbohydrate metabolism, individual amino acids and protein quality, and lipid composition and fatty acid metabolism.

Vitamin, mineral and nutrient deficiencies are rare in the U.S. today due to food fortification, but the challenge for the future will be to combat the problems of overnutrition with fat and calories. In order to understand the problems of obesity and overnutrition, it is important to realize that all food components can be interconverted and stored as fat when there are excess calories. In addition, the efficiency with which extra calories are converted to fat is genetically determined. Therefore, there is a gene-nutrient interaction of importance with every nutritional disorder.

The basic processes of oxidant stress have influenced both plant and human evolution. Plants contain a number of natural antioxidants and humans have developed endogenous enzyme systems, as well as endogenously produced antioxidants which are relevant to the nutritional environment. For example, humans do not manufacture vitamin C as do most other animal species due to its abundance in a plant-based human diet. Scurvy only occurred once man moved to the food supplies of the last few hundred years that are significantly less diverse when compared to the ancient biodiverse diet of 50,000 to 100,000 years ago.

Plants also contain a number of unique phytochemicals not available as supplements. These phytochemicals stimulate the cells of our bodies to develop enzymes to metabolize these substances. For example, someone taking 500 mg per day of vitamin C has a different panel of metabolizing enzymes in their liver than someone taking only 20 mg per day of vitamin C. The interaction of the nutritional environment and the human body occurs at the molecular genetic, cellular, organ and whole body levels.

Modern dietary recommendations need to consider the basic science of nutrition and the current problems of overnutrition, obesity, and chronic disease. Recommendations for dietary intake among populations often take the form of pyramids with the base of the basis of the diet.
The base of the USDA pyramid developed in the late 1980’s consists of cereals and grains without an emphasis on the fiber content of those grains. The fruits and vegetables appear on the second level and are two separate groups. In a new pyramid developed in 1997 by the UCLA Center for Human Nutrition, a modified plant-based diet is recommended. The base consists of fruits and vegetables to provide unique phytonutrients for chronic disease prevention. The second level emphasizes high fiber cereals and grains to provide the benefits of fiber from these foods as well as from fruits and vegetables. The protein level is made up of low fat protein choices from both the plant and animal kingdoms. The top tier of the USDA pyramid has only dots representing fats and sweets with the mixed message "use sparingly". The top tier of the new California Pyramid emphasizes taste enhancers including olives, avocados, garlic, onion, nuts, cheese, chili peppers, and small amounts of monounsaturate or omega-3-rich oils needed to enhance taste. The overall fat recommendation of the USDA pyramid is 30% or less of calories from fat, while the California pyramid reflects the decreased fat intake in the population recommending 20% or less of calories from fat.

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