The 2015 Dietary Guidelines for Americans are due to be published later this year. The Scientific Report of the 2015 Dietary Guidelines Advisory Committee (DGAC) released February 23 this year suggested that we may see important changes of direction in certain areas.
Since the publication of the 2010 Dietary Guidelines important scientific data has emerged suggesting that the role of sodium intake, different types of dietary fats, carbohydrates, and added sugars may have to be reevaluated.
In general, dietary guidelines encourage people to focus on eating a healthful diet. Such a diet focuses on foods and beverages that guarantee adequate nutrition, achieve and maintain a healthy weight, promote health, and prevent disease.
Recently, the Academy of Nutrition and Dietetics published their commentary on the Scientific Report of the 2015 DGAC. The Academy is the largest association of food and nutrition professionals in the United States.
Interestingly, the Academy suggests a major revision of key issues that are likely to affect our view on the relationship between diet and heart health.
Diet and Heart Health
Initially, the dietary guidelines were born in an era where the mortality from coronary heart disease (CHD) was rising at a very rapid rate. At the beginning of the 20th century, acute heart attack (myocardial infarction) was relatively unknown. Fifty years later it was recognized as the most common cause of death in developed countries.
Public authorities were helpless. Here was a disease that brought an end to the lives of many people in their prime. It tragically, without warning, robbed wives of their husbands, husbands of their wives, and children of their parents. Something had to be done.
It soon became apparent that the risk of CHD was correlated with blood levels of cholesterol. Therefore, not surprisingly, blood cholesterol became a target in the fight against CHD.
Ever since the beginning of the 1960s, “eat less fat, in particular, less saturated fat, and cholesterol” has been the message from public health authorities and medical professionals. Food manufacturers have played along by emphasizing low-fat food varieties and highlighting “low-fat” as an important trademark
For the last 30 years, we have seen a dramatic fall in mortality from CHD and age-adjusted incidence has dropped as well. This is due to many factors, one of them likely being the lowering of blood cholesterol in the population.
However, the burden of CHD is still very high, partly due to the aging of the population. Furthermore, we have seen a rapid rise in obesity and related disorders such as type 2 diabetes, obstructive sleep apnea, non-alcoholic fatty liver disease, atrial fibrillation and some types of cancer.
The Academy’s Comments
Several issues addressed in the recent Academy of Nutrition and Dietetics’ commentary to the DAGC are of particular interest. These deal with salt intake, red meat, dietary cholesterol, saturated fats and added sugar.
The Academy highlights the fact that there is “a distinct and growing lack of scientific consensus on making a single sodium consumption recommendation for all Americans, owing to a growing body of research suggesting that the low sodium levels recommended by the DGAC are actually associated with increased mortality for healthy individuals“.
There are several studies that have suggested that diets restricted in sodium may be beneficial for individuals with high blood pressure. However, the Academy is concerned that the recent DGAC’s scientific report appears to use conclusions from these studies as “a basis for making a general recommendation that all American adults consume less than 2,300 mg/day of sodium.”
The DGAC appears to recognize that it may be difficult to identify those who may benefit from restricting dietary salt and sodium. Therefore, in light of the growing evidence that sodium restriction at the level recommended may cause harm, adopting such a recommendation to the general population appears controversial.
The DGAC recommends that the US population should be encouraged and guided to consume dietary patterns that are rich in vegetables, fruits, whole grains, seafood, legumes, and nuts; moderate in low-fat dairy products and alcohol; lower in red and processed meat; and low in sugar-sweetened foods and beverages and refined grains.
The Academy does not “interpret that recommendation as impugning the healthfulness of red meat or its place in recommended meal patterns…”
The Academy points out that approximately 80 percent of Americans meet the intake recommendation for animal proteins, mainly based on the consumption of meat, poultry and eggs. However, “data from NHANES for the consumption of red meat alone suggests that American adults on average eat almost as much red meat per week (20 oz) as the USDA recommends for meat, poultry, and eggs combined (26 oz)“.
The Academy seems to agree “(a) that red meat consumption exceeds recommendation for most subgroups and (b) that a greater share of recommended protein consumption should be met by seafood, legumes, and nuts.”
The Academy “supports the decision by the 2015 DGAC not to carry forward previous recommendations that cholesterol intake be limited to no more than 300 mg/day, as available evidence shows no appreciable relationship between consumption of dietary cholesterol and serum cholesterol.”
The Academy also lauds the DGAC for its willingness to update positions based on new evidence. However, whether such an obvious act is praiseworthy or not is debatable.
The Academy writes; “It has been said that the unit of measurement for scientific progress is scientific error. Every new discovery proves old conclusions wrong, and every incorrect conclusion of the past marks new knowledge that has taken its place. The Committee’s willingness to update positions based on new evidence is laudable.”
“In the spirit of the 2015 DGAC’s commendable revision of previous DGAC recommendations to limit dietary cholesterol, the Academy suggests that HHS and USDA support a similar revision deemphasizing saturated fat as a nutrient of concern. While the body of research linking saturated fat intake to the modulation of LDL and other circulating lipoprotein concentrations is significant, this evidence is essentially irrelevant to the question of the relationship between diet and risk for cardiovascular disease.”
The above conclusion suggests a major change of direction in how health authorities view the role of dietary fats in health and disease.
The Academy writes, “We commend the DGAC on a thorough and accurate review of the current best evidence with regard to the body of evidence relating dietary fats to cardiovascular disease outcomes. However, we are concerned that the evidence does not lead to the conclusion that saturated fats should be replaced with polyunsaturated fats for the greatest health benefit.”
The Academy arguments that “carbohydrate intake conveys a greater amount of cardiovascular disease risk than does saturated fat”.
It is concluded “that the substitution of polyunsaturated fat for carbohydrate will result in a lesser net risk for cardiovascular disease than if polyunsaturated fat were substituted for saturated fat. This is true because carbohydrate contributes a greater amount to the risk for cardiovascular disease than saturated fat, so the replacement of carbohydrate will necessarily result in a greater improvement in risk”.
“Therefore, it appears that the evidence summarized by the DGAC suggests that the most effective recommendation for the reduction in cardiovascular disease would be a reduction in carbohydrate intake with replacement by polyunsaturated fat.”
This simplified recommendation would also aid in creating a consistent overall message of the DGA, allowing for consumer messaging to focus on benefits of decreasing added sugars in the diet to reduce cardiovascular disease, obesity, and type 2 diabetes, consistent with the conclusion statements in the added sugars section of the Scientific Report.
The Academy’s view on added sugar is very clear;
Of all the crosscutting topics reviewed, the evidence is strongest that a reduction in the intake of added sugars will improve the health of the American public. The identification and recognition of the specific health risks posed by added sugars represents an important step forward for public health. We recommend that these risks and recommendations be featured prominently in the 2015 Dietary Guidelines for Americans.