Dietary Reference Intakes
For Energy, Carbohydrate, Fiber, Fat, Fatty Acids, Cholesterol, Protein, and
Institute of Medicine
September 5, 2002
Joanne R. Lupton, Ph.D.
Regents Professor and University Faculty Fellow and
William W. Allen Endowed Chair in Nutrition, Texas A&M University
Chair, Panel on Dietary Reference Intakes for Macronutrients
Good morning. On behalf of the National Academies, I would like to welcome those of you in the room as well as those listening on the Web. Thank you for joining me and some of my fellow panel members to release a report that we hope will guide policy-makers, health professionals, and others as they grapple with complex nutritional issues.
Since 1941, the Food and Nutrition Board of the National Academies has set Recommended Dietary Allowances on the types and quantities of nutrients that are needed for healthy diets. Over the past eight years the board has implemented an expanded system for determining the RDAs and other nutrient-based reference values; this system is called Dietary Reference Intakes or DRIs. The report we are releasing today is the latest in a series on DRIs, developed jointly by American and Canadian scientists. It focuses on carbohydrate, fiber, fat, the various fatty acids, cholesterol, protein, and amino acids, which collectively are called the macronutrients. In addition, the report includes recommendations for energy expenditure and physical activity. Our findings and recommendations are based on a comprehensive review of the scientific literature in this area.
Unlike vitamins and minerals, which perform specific functions to meet the body's needs, most of these macronutrients supply energy for daily activity. Fats, carbohydrates, and proteins can substitute for one another to some extent to meet the body's energy needs. At the same time, a growing amount of evidence suggests that eating excessive amounts of some of the macronutrients can lead to health problems, including obesity, heart disease, and diabetes, although questions remain about the links between some of the macronutrients and disease. It seems that every year brings many more studies on fats, carbohydrates, and proteins, and while these studies sometimes reinforce each other's results, other times the results seem contradictory. This panel reviewed thousands of studies, determined where the data conflict and why, and based its conclusions and recommendations on the most scientifically compelling evidence. We hope that our report brings some science-based clarity to the complicated and often confusing debate over carbohydrates, fats, and protein.
So, how much of these macronutrients does one need to consume on a daily basis to ensure good health? To answer that question, we offer both specific values as well as ranges for consumption of fats, carbohydrates, and proteins. The ranges are new and were developed to achieve a nutritionally adequate diet while minimizing the risk for developing chronic disease. The report also emphasizes the critical importance that physical activity and fitness have on maintaining health. For the first time, we recommend levels of energy expenditure through physical activity to maintain a lower risk of developing chronic disease.
I will briefly review our main recommendations and then we will take questions.
People need certain amounts of each of the main kinds of macronutrients for good health, but evidence suggests that too much or too little of any is associated with chronic disease or other health problems. To reduce the risk of chronic illness, we recommend that adults get 45 to 65 percent of their calories from carbohydrates and 20 to 35 percent of their calories in the form of fat. We suggest that no more than 25 percent of total calories should come from added sugars (essentially soft drinks, pastries, cookies, candy, and other foods and beverages to which sugar is added during production). Protein also is a source of energy as well as a major component of cells and tissues. To complement the ranges for fats and carbohydrates, adults should get 10 to 35 percent of their energy from protein.
Fat is essential in the diet for promoting absorption of some vitamins and helping build some tissues. Monounsaturated and polyunsaturated fatty acids reduce blood cholesterol levels and help lower the risk for heart disease. The report sets recommended daily intake values for alpha-linolenic acid, which is an omega-3 fatty acid, and linoleic acid, which is an omega-6 fatty acid. Adult men should get 17 grams of linoleic acid and 1.6 grams of alpha-linolenic acid per day. Adult women should take in 12 grams of linoleic acid and 1.1 grams of alpha-linolenic acid each day. The report also lists intake values for children and pregnant and lactating women.
Certain kinds of fats, however, provide no known beneficial role in preventing chronic disease. These fats include saturated fat, trans fatty acids, and cholesterol. Moreover, research suggests that these fats raise the level of low-density lipoproteins in the blood and hence the amount of "bad" cholesterol, which has been linked to heart disease. Because these fats are not required at any level in the diet, the maximum safe intake level for each would be zero. All-out avoidance of them, however, would require extreme changes in the typical diet in the United States and Canada, and thus would make it difficult to meet other important nutritional guidelines. Therefore, we recommend keeping consumption of saturated fat, trans fatty acids, and cholesterol as low as possible while maintaining a nutritionally adequate diet.
The lowest specific amount of carbohydrate that people should consume each day is 130 grams to maintain normal levels of glucose in the brain. To give you an idea of how much that is, a slice of bread contains about 15 grams of carbohydrate, while a glass of skim milk contains 12 grams. This recommendation is based on the minimum amount of carbohydrate needed to produce enough glucose for the brain to function properly. The vast majority of Americans and Canadians consume more than this amount each day. The recommended intakes for pregnant and lactating women are higher, at 175 grams and 210 grams per day, respectively.
The report stresses the need for people to moderate their consumption of added sugars. When people consume large amounts of added sugar through foods and beverages, they frequently either take in excess calories, which can contribute to obesity if these calories are not expended through physical activity, or they tend to eat fewer foods that contain desirable amounts of vitamins, minerals, or other essential nutrients, thus contributing to a poorer overall diet.
The recommended intakes for protein for adults remain the same as previously established values. The recommended intake for adult men and women is 0.8 grams of protein per kilogram of body weight. A 70-kilogram woman (about 150 pounds), for example, should eat 56 grams of protein each day. She might accomplish this goal by drinking two 8-ounce glasses of skim milk, eating a slice each of cheese and ham in a sandwich, and having one 3-ounce serving of meat at dinner. The recommended intakes for children are set according to age and body weight. We also set recommended values for pregnant and lactating women, which are somewhat higher than previous recommendations.
There is little scientific literature on the health effects of consuming very-high-protein diets, and the results of existing studies are conflicting. Therefore, we were not able to determine a specific safe maximum level for protein consumption. The intake range of 10 to 35 percent set for protein provides a reasonable guideline for how much protein should be part of a balanced, healthy diet.
For the first time, we set intake values for the nine indispensable amino acids. The values depend on gender and age. Based on these values, we developed a recommended scoring pattern designed to compare the quality of various protein sources. We also set intake levels for pregnant and lactating women.
While plant proteins sometimes contain lesser concentrations of certain indispensable amino acids, people who consume a varied vegetarian diet can get the same quality of protein and similar amounts of nitrogen as yielded by animal protein or a mixed diet. Therefore, we did not recommend separate protein or amino acid intake levels for vegetarians, but provide guidance on using the protein quality scoring pattern to determine how much of various protein sources to use.
Our panel also proposes a new definition of total fiber based on earlier proposed definitions it developed for dietary fiber and functional fiber. The decision to do so stemmed from the variety of competing and sometimes vague definitions of fiber currently in use worldwide and the increasing number of new products being marketed as fiber.
We define dietary fiber as nondigestible carbohydrates and lignin that are found in plants. Functional fiber consists of synthetic or isolated, nondigestible carbohydrates that have beneficial physiological effects in humans. Total fiber is the sum of dietary fiber and functional fiber. To be called a functional fiber, these fibers will need to demonstrate a physiological role that can be linked to beneficial health effects, such as lowering blood cholesterol or maintaining appropriate blood glucose levels. Up to age 50, an intake of 38 and 25 grams per day of total fiber for men and women respectively may help ward off heart disease. Because of the decline in food consumption after age 50, the panel recommends that men over 50 consume at least 30 grams of total fiber per day, and women, 21.
The panel determined estimated energy requirements for both men and women based on height, weight, age, and four levels of physical activity. These estimated energy requirements focus on how much energy a person needs to expend to have the best level of physical activity and cardiovascular health. They are not intended to be used as targets by people who are trying to lose weight.
In addition, because physical activity has been associated with preventing cardiovascular disease, the panel set a recommended level of physical activity at one hour of moderately intense activity each day in order to get maximum benefits from physical activity. Brisk walking is a good example of moderately intense activity. Our recommendation is double the daily half-hour goal set by the Surgeon General in 1996. We recognize that the lifestyles of many in the United States and Canada might make this goal seem difficult to achieve. More intense exercise, such as running or cycling, requires shorter duration and less frequency.
This concludes my opening statement. My colleagues and I will now take your questions. Those of you listening to our webcast can send in questions by e-mail, using a link on the National Academies home page. We ask those of you in the room to step to a microphone and identify yourself and your organization when asking your question. We'll begin with a question in the room.