The US Institute of Medicine yesterday released new guidelines on healthy eating in a bid to reduce the growing levels of cardiovascular disease in the US, guidelines which have been broadly welcomed by the US food industry.
The report by the IOM’s Food and Nutrition Board stresses the need to combine a balanced diet with regular exercise, and gives recommended calorie intakes for individuals of all heights and weights.
The report suggests that the best way to supply the body’s daily energy and nutritional needs while minimising risk for chronic disease is to restrict calorie intake to 45 to 65 per cent from carbohydrates, 20 to 35 percent from fat and 10 to 35 per cent from protein. To maintain cardiovascular health at a maximal level, regardless of weight, adults and children should also spend a total of at least one hour each day in moderately intense physical activity, the report suggests, a figure which is double the daily goal set out in a report from the US Surgeon General in 1996.
Earlier guidelines called for diets with 50 per cent or more of carbohydrate and 30 per cent or less of fat. The protein intake recommendations are the same. The new acceptable ranges for children are similar to those for adults, except that infants and younger children need a slightly higher proportion of fat - 25 to 40 per cent of their caloric intake – according to the panel that wrote the report.
"We established ranges for fat, carbohydrates and protein because they must be considered together," said panel chair Joanne Lupton, professor of nutrition at Texas A&M University. "Studies show that when people eat very low levels of fat combined with very high levels of carbohydrates, high-density lipoprotein concentration, or ‘good’ cholesterol, decreases. Conversely, high-fat diets can lead to obesity and its complications if caloric intake is increased as well, which is often the case. We believe these ranges will help people make healthy and more realistic choices based on their own food preferences."
The new guidelines were drawn up because of the new evidence about nutrient intake which has emerged since the last recommendations were made in 1989. Former guidelines focused on RDAs, recommended dietary allowances, which were set out to ensure sufficient nutritional intake; the new guidelines talk instead about DRIs, or Dietary Reference Intakes, which are an expansion of the old system in that they include indicators of good health and the prevention of chronic disease, as well as possible adverse effects of over-consumption.
Thousands of scientific studies linking excessive or inadequate consumption of fats, carbohydrates and protein with increased risk for dietary deficiency diseases, obesity, heart disease, diabetes, and other chronic illnesses were studied by the panel in order to update the guidelines. The resulting DRIs include not only recommended intakes, intended to help individuals meet their daily nutritional requirements, but also tolerable upper intake levels (ULs) that help them avoid harm from consuming too much of a nutrient.
Clarifying sugar, fat intake
Both children and adults should consume at least 130 grams of carbohydrates each day, the report says. However, this newly set RDA is based on the minimum amount of carbohydrates needed to produce enough glucose for the brain to function, and most people regularly consume far more. Basing its recommendations on the evidence that people whose diets are high in added sugars have lower intakes of essential nutrients, the report suggests that added sugars (such as those found in confectionery or soft drinks) should comprise no more than 25 per cent of total calories consumed.
The IOM panel also sought to clarify the situation with regard to fat, since there is a general perception that all fat is bad and should be avoided. While fat is a major source of energy for the body and can aid in the absorption of essential vitamins, diets which are high in fat usually lead to increased levels of saturated fat, which can raise the amount of low-density lipoprotein and the level of "bad" cholesterol in the bloodstream, increasing the risk of heart disease.
But because completely eliminating saturated fat and cholesterol from the typical diet in the United States or Canada would make it very difficult to meet other nutritional guidelines, the panel recommended keeping consumption as low as possible while maintaining a nutritionally adequate diet.
On the other hand, monounsaturated and polyunsaturated fatty acids, also present in fat, can reduce blood cholesterol levels and thus lower the risk of heart disease when they replace saturated fats in the diet. Food is the sole source of two essential fatty acids – alpha-linolenic acid and linoleic acid – since the body cannot synthesise either substance, the report points out. It sets the recommended intakes for linoleic acid, present in high levels in vegetable oils such as safflower oil or corn oil, at 17 grams per day for men and 12 grams per day for women based on average intakes in the United States, while the figures for alpha-linolenic acid, found in milk and some vegetable oils such as soybean and flaxseed oils, are 1.6 and 1.1 grams per day for men and women respectively.
The nutrition panel also reiterated its statement on trans fatty acid, published in July at the request of the FDA which was investigating whether such fat content should be labelled. That statement said that the substance, found in partially hydrogenated vegetable oils such as those used in many margarines and shortenings, can increase the risk of heart disease by increasing ‘bad’ cholesterol levels. It added that since trans fatty acids had no known health benefit, there was no safe level of consumption and they should be avoided if possible. However, since they are used in so many foods, banning them completely would be impractical and make it difficult for consumers to get a nutritionally adequate diet.
Fibre appears for the first time
The new guidelines are also the first to provide recommended intake levels for fibre and are based on studies that show a low-fibre diet can cause an increased risk for heart disease. The panel acknowledged that there was a growing body of evidence to suggest that fibre in the diet could also help prevent colon cancer and promote weight control, but stressed that the data was as yet insufficient to make a concrete recommendation.
That said, the panel set a recommended daily intake for total fibre for adults under the age of 50 at 38 grams for men and 25 grams for women; for men and women over 50, the RDI is 30 and 21 grams per day respectively. The report also provides recommended intakes for children and teenagers.
Fibre has long been a buzz word for the food industry, and there are many products whose marketing campaigns are based around a high fibre content. However, the panel stressed that since there is no uniform definition of fibre set out in law in the US, many of these claims could be erroneous. It therefore suggests a definition of fibre: total fibre should be seen as the combination of both dietary (the edible but non-digestible component of carbohydrates and lignin naturally found in plant food) and functional fibre (which is isolated or extracted from natural sources or is synthetic).
Dietary fibre can be found in cereal bran, flaked corn cereal, sweet potatoes, legumes and onions, while functional fibres are products such as pectin extracted from citrus peel and used as a gel that is the basis for jams and jellies. Importantly, the panel sought to exclude from the definition of functional fibre all fibre-like products which cannot be shown to have proven health benefits. While these recommendations are just that, the panel said it hoped that the regulators in the US would adopt the definitions in law.
Expanded guidelines for protein
Also for the first time, the new guidelines establish age-based requirements for all nine of the essential amino acids found in dietary protein. Values are included for pregnant women, infants and children based on their special needs. Using new data, the report reaffirms previously established recommended levels of protein intake, which is 0.8 grams per kilogram of body weight for adults. Recommended intake of protein during pregnancy has also been increased.
Since the data on the potential for high-protein diets to produce chronic or other disease was often conflicting or inadequate, the panel said that tolerable upper intake levels for consumption could not be determined for protein or for the individual amino acids. However, given the lack of data on over-consumption for some of these amino acids and protein, it said that caution was warranted in consuming levels significantly above those normally found in foods.
The food industry has been quick to react to the guidelines, which have been broadly welcomed. Robert Earl, senior director of nutrition policy for the National Food Processors Association (NFPA) – the voice of the US food industry on such matters – said: "The NFPA applauds the FNB and this report for its focus on providing sound, actionable nutrition recommendations for the food industry, health professionals and policymakers. The report provides important information that can be used to develop food and nutrition policy to educate consumers on how to create healthful diets.”
He said that the report's specific dietary intake recommendations for fatty acids, dietary fibre and essential amino acids were of particular importance, as were the definitions of dietary, functional and total fibre. “This information will ultimately be useful to consumers in helping them to understand how certain nutrients from foods are valuable for the roles they play in basic nutrition and for their additional health benefits," he said.
The need for exercise was also of vital importance, he said. "The FNB report underscores the recommendations of government and nutrition experts that individuals should eat a wide variety of foods, consumed in moderation, in combination with physical activity. In fact, the report contains recommendations for levels of physical activity to decrease the risk of various chronic diseases. The report clearly makes the case that daily physical activity is of vital importance in the creation and maintenance of a healthful diet," he concluded.
The FNB study was sponsored by the US Department of Health and Human Services Office of Disease Prevention and Health Promotion, Health Canada, the US Food and Drug Administration, the National Institutes of Health, the Centers for Disease Control and Prevention, the US Departments of Agriculture and Defense, the Institute of Medicine, the Dietary Reference Intakes Private Foundation Fund and the Dietary Reference Intakes Corporate Donors' Fund, contributors to which include Roche Vitamins, Mead Johnson Nutrition and M&M Mars.
The full report can be read on the internet at the National Academies website.