Scientific Report of the 2020 Dietary Guidelines Advisory Committee: Evidence on Diet and Health Part Four

 

Our series on the scientific report of the 2020 Dietary Guidelines Advisory Committee continues, this time with a look at Diet and Health Relationships: Individuals Ages 2 Years and Older. Have you read all the previous installments yet? Just in case you haven't, I've detailed them below!

  1. Executive Summary
  2. Setting the Stage and Integrating the Evidence
  3. Methodology
  4. Evidence on Diet and Health Part One: Current Dietary Intakes Through the Life Course
  5. Evidence on Diet and Health Part Two: Pregnancy and Lactation
  6. Evidence on Diet and Health Part Three: Birth to Age 24 Months

And now, on to Diet and Health Relationships: Individuals Ages 2 Years and Older!

This one has the following chapters...

  • Dietary Patterns
  • Dietary Fats and Seafood
  • Beverages
  • Alcoholic Beverages
  • Added Sugars
  • Frequency of Eating
  • USDA Food Patterns for Individuals Ages 2 Years and Older

Let's begin with Dietary Patterns. "Traditionally, associations of diet to health have focused primarily on a single nutrient or food and an identified health outcome. Since the early 2000s, the focus for quantifying dietary exposures has moved from single nutrients or foods to dietary patterns as a way to more comprehensively represent the totality of the diet and nutrient profiles."

"Dietary patterns are defined as the quantities, proportions, variety, or combination of different foods, drinks, and nutrients in diets, and the frequency with which they are habitually consumed." These patterns are derived largely using two different methods, index-based patterns and exploratory patterns.

This chapter is guided by the following questions...

  1. What is the relationship between dietary patterns consumed and risk of cardiovascular disease?
  2. What is the relationship between dietary patterns c onsumed and growth, size, body composition, and risk of overweight and obesity?
  3. What is the relationship between dietary patterns consumed and risk of type 2 diabetes?
  4. What is the relationship between dietary patterns consumed and bone health?
  5. What is the relationship between dietary patterns consumed and risk of certain types of cancer?
  6. What is the relationship between dietary patterns consumed and neurocognitive health?
  7. What is the relationship between dietary patterns consumed and sarcopenia?
  8. What is the relationship between dietary patterns consumed and all-cause mortality?

Did you know that this was the first time the Committee explored the link between dietary patterns and all-cause mortality?

And now to the main highlight from this chapter: "A consistent dietary pattern associated with beneficial outcomes was present across all 7 of the reviewed questions for which grades of variable strength were assignable: higher intake of vegetables, fruits, legumes, whole grains, low- or non-fat dairy, lean meat and poultry, seafood, nuts and unsaturated vegetable oils, and low consumption of red and processed meats, sugar-sweetened foods and drinks, and refined grains. Dietary patterns associated with adverse or detrimental outcomes included higher intake of red and processed meats, sugar- sweetened foods and beverages, and refined grains. A notable new observation was an association of the main components of the aforementioned dietary pattern with lower all-cause mortality, a finding the Committee graded as Strong."

This chapter concludes, "these public health messages are vital, especially in an era undergoing an epidemic of non-communicable diseases, including obesity, type 2 diabetes, CVD, cancer, sarcopenia, and dementias, and that pose potential further immunological risks associated with infectious diseases as well. These chronic diseases often have their origins early in life, highlighting the importance of initiating and maintaining a healthy diet across the life course."

And now onto the next chapter, Dietary Fats and Seafood! This one had a little bit of a plot twist, outlined by the Committee here "Although the Committee initially sought to conduct its dietary fats review on a range of health outcomes including CVD, all-cause mortality, certain types of cancer, and neurocognitive health, it ultimately chose to focus on CVD outcomes." They explored the impact of seafood on health largely due to seafood's positive associations with heart and neurocognitive health.

Three questions drove this section, and I've copied them below...

  1. What is the relationship between types of dietary fat consumed and risk of cardiovascular disease?
  2. What is the relationship between seafood consumption during childhood and adolescence (up to 18 years of age) and risk of cardiovascular disease?
  3. What is the relationship between seafood consumption during childhood and adolescence (up to 18 years of age) and neurocognitive development?

Now let's move right on to this chapter's conclusions...

"Fats are an important component of the American diet, contributing about one-third of the total calories consumed after infancy. The types and food sources of fats consumed have distinct metabolic and health effects."

"The Committee concluded that reducing saturated fat intake and replacing it with unsaturated fats, particularly polyunsaturated fat, lowers the incidence of CVD in adults. Also, the replacement of saturated with unsaturated fats in the diet reduces serum total and LDL-C in adults and children, particularly boys."

"Intake of omega-3 polyunsaturated fatty acids, particularly EPA and DHA from food sources such as seafood and algae, lowers blood triglycerides, and in adults, is associated with lower risk of CVD. Intake of food sources of omega-6 polyunsaturated fatty acids such as some vegetable oils, lowers blood total and LDL-C, and LA but not AA, intake may be associated with lower risk of CVD in adults."

"Dietary patterns that include lower intake of dietary cholesterol are associated with reduced risk of CVD."

Remember, humans don't need any cholesterol or saturated fats -- our bodies can synthesize them from dietary substrates. Therefore "the Committee recommends that dietary cholesterol and saturated fat intake be as low as possible within a healthy dietary pattern, and that saturated fat intake be limited to less than of 10 percent of total energy intake[...] This recommendation applies to adults and children ages 2 years and older."

Unfortunately, there was often not enough evidence to draw conclusions about seafood intake and brain health and the consumption of seafood's impact on the health of children and teens, though no adverse associations were demonstrated.

"The Committee recommends that the seafood-related guidance of the 2010 and 2015 Committees remain in place, with slight modifications: Two or more servings of cooked seafood per week are recommended for ages 2 years and older to ensure intake of key nutrients and as part of an overall healthy dietary pattern; serving sizes vary based on age (see FDA guidance). Choices of fish and seafood with emphasis on species higher in omega-3 polyunsaturated fatty acids and with low methylmercury and are advised."

And finally, "The 2020-2025 Dietary Guidelines for Americans should contain information on amounts and types of seafood to consume as well as those to avoid based on the methylmercury content. Special emphasis should be made with regard to the birth to age 24 months age group and women who are pregnant or lactating. The Committee recognizes that recommendations to increase seafood consumption by the American public can have environmental consequences and such impacts should be evaluated in the development of the Dietary Guidelines for Americans."

Now, on to the next chapter, Beverages! The report begins, "Beverages, broadly defined as any type of energy or non-energy-yielding drink, substantially contribute to the dietary patterns of Americans in both favorable and adverse ways." With that in mind, the Committee posed 2 questions to guide this chapter...

  1. What is the relationship between beverage consumption and achieving nutrient and food group recommendations?
  2. What is the relationship between beverage consumption and growth, size, body composition, and risk of overweight and obesity?

So let's dive right in to the answers!

"this is the first time that a Dietary Guidelines Advisory Committee has directly examined the relationship between beverage consumption and health outcomes related to growth, size, body composition, and risk of overweight and obesity," conducting separate analyses on different beverages like milk, juice, etc.

"When nutrient-rich beverages are incorporated into the diet, it will be important to be mindful of their contribution to total energy intake [...] Among the beverages examined in the NESR systematic review, only SSB [sugar-sweetened beverage] intake was associated with adiposity and this held in both children and adults."

"No significant association was observed between consumption of [Low/No-Calorie Sweetened Beverages, a.k.a. LNCSB] and adiposity outcomes in children, but their intake was associated with reduced adiposity in adults."

"Lastly, beverage patterns, defined as the quantities, proportions, variety or combinations of different beverages in the diet, were not examined by the 2020 Dietary Guidelines Advisory Committee due to a lack of available literature."

And that's the end of the beverage section. Next up is Alcoholic Beverages!

Let's begin with some context about current alcoholic beverage consumption.

"Alcohol consumption in the United States has increased during the past 20 years, and 41 states exceed Healthy People 2020 limits for per capita alcohol consumption. Fifty-six percent of adults ages 21 years and older report past-month alcohol consumption, and nearly half of current drinkers across most age categories report past-month binge drinking. Binge drinking itself has increased, including among middle- and older-aged adults, as has mortality from fully alcohol-attributable causes of death, including alcoholic liver disease. Other than energy (i.e., calorie) intake, alcohol provides little nutritional value. Among U.S. adults, alcohol accounts for approximately 5 percent of energy intake, or approximately 9 percent of energy intake among those who drink. Among those who consume excessive amounts of alcohol, the percent of energy intake may be considerably higher, and binge drinking is associated with obesity."

"Because alcohol is not a component of USDA food pattern guidance, its added energy is discretionary and should be considered in the present context of high and increasing obesity prevalence."

Two questions shaped this chapter...

  1. What is the relationship between alcohol consumption and achieving nutrient and food group recommendations?
  2. What is the relationship between alcohol consumption and all-cause mortality?

Let's see what the Committee concluded!

"Many U.S. adults consume alcohol excessively, and an even higher proportion consume alcohol at a level exceeding 2015-2020 Dietary Guidelines for Americans recommended limits for 'drinking in moderation' during days when alcohol is consumed [...] excessive alcohol consumption is a leading behavioral risk factor for a variety of morbidity and mortality outcomes, social harms, and economic costs."

"Despite limitations of the observational evidence base, the conclusion that higher consumption is associated with increased risk compared to lower consumption is affirmed by outcomes that are fully alcohol-attributable (alcoholic cirrhosis), or outcomes for which alcohol is a predominant risk factor with short and relatively easily studied exposure-outcome relationships (e.g., motor vehicle crashes, falls, drownings)."

"Although the 2/1 levels (that have been in previous Dietary Guidelines for Americans since 1990) constitute reasonably low risk, evidence justifies tightening guidelines for men."

"Overall, alcohol is an unhealthy substance, and the United States population is far from achieving alcohol consumption levels that would meaningfully reduce alcohol-related harms. Alcohol can be consumed at low levels with relatively low risk, and is consumed by U.S. adults for a variety of reasons. However in terms of health, among those who consume alcohol, drinking less is better for health than drinking more."

Whew! That one was intense! Next on the list is the Added Sugars chapter. The Committee defines added sugars "according to the 2016 U.S. Food and Drug Administration (FDA) guidance, which is sugars that are either added during the processing of foods, or are packaged as such" and asserts "Guidance on added sugars is of great relevance because of the high prevalence in the United States of overweight and obesity, type 2 diabetes, cardiovascular disease (CVD), and adiposity-related cancers."

This section of the report focuses on 3 questions...

  1. What is the relationship between added sugars consumption and achieving nutrient and food group recommendations?
  2. What is the relationship between added sugars consumption and risk of cardiovascular disease?
  3. How much added sugars can be accommodated in a healthy diet while still meeting food group and nutrient needs?

After exploring each of these questions, the Committee concludes, "Taking into account both the 2015 and 2020 Committee evidence reviews, relative to the goal of improving the health of a population in which the prevalence of overweight and obesity is high, the addition of sugar to the diet raises concerns about the potential risk of increasing unhealthy weight gain and, in turn, increasing risk of obesity-related health outcomes [...] reducing the amount of added sugars in the diet, through either changes in consumer behavior or in how food is produced and sold, or through food policy, is an achievable objective that could improve population health."

And herein lies a big change from previous recommendations from the Committee. Now, "the Committee suggests that for adults and children ages 2 years and older, a recommendation of less than 6 percent of energy from added sugars is more consistent with a dietary pattern that is nutritionally adequate while avoiding excess energy intake than is a pattern with less than 10 percent energy from added sugars."

After added sugars, we just have 2 chapters to go! Next up is Frequency of Eating. "Although eating behavior is usually thought of in terms of the types and amounts of foods ingested, the frequency of eating is an equally important factor."

This chapter explores the interaction between frequency of eating and:

  • Growth
  • Achieving nutrient and food group recommendations
  • Body size and composition
  • Overweight and obesity
  • All-cause mortality
  • Cardiovascular disease
  • Type 2 diabetes

In order to do this, the Committee outlines 5 different questions...

  1. What is the relationship between the frequency of eating and achieving nutrient and food group recommendations?
  2. What is the relationship between the frequency of eating and growth, size, body composition, and risk of overweight and obesity?
  3. What is the relationship between the frequency of eating and all-cause mortality?
  4. What is the relationship between the frequency of eating and risk of cardiovascular disease?
  5. What is the relationship between the frequency of eating and risk of type 2 diabetes?

And now here are the highlights of this chapter's summary...

"The 3 main components that characterize a person’s eating behavior are the frequency, types, and amounts of foods ingested."

"The 2020 Committee is the first to directly address the question of frequency of eating."

"The NESR review [Nutrition Evidence Systematic Review] did not yield specific answers to the questions concerning the relationship between frequency of eating and health outcomes of obesity, all-cause mortality, risk of cardiovascular disease, or risk of type 2 diabetes. This was primarily due to the limited availability of high-quality data. The Committee cannot therefore make recommendations to the Departments on frequency of eating and health."

"The Committee was able to address the relationship between the frequency of eating and achieving nutrient and food group recommendations. [...] Americans who reported consuming an average of 3 meals per day had a higher diet quality compared to those consuming 2 meals per day."

"The Committee’s findings also suggest that following a dietary pattern that reduces snacking and emphasizes meals, both primarily comprised of foods and beverages that contribute to nutrient and food group recommendations, can help align eating patterns with dietary guideline recommendations."

And now for the final chapter in Part D: Evidence on Diet and Health: Diet and Health Relationships: Individuals Ages 2 Years and Older -- USDA Food Patterns for Individuals Ages 2 Years and Older.

"The 2020 Dietary Guidelines Advisory Committee pursued systematic reviews to identify combinations of foods that have been associated with lower risk of all-cause mortality and a number of important health outcomes across the lifespan (see Part D. Chapter 8: Dietary Patterns). Translating this evidence into actionable guidance for the public at large means that the Committee also must determine whether combinations of foods within a pattern meet goals for nutrient adequacy."

"The 2020 Committee used recommendations provided by the 2017 National Academies of Science, Engineering, and Medicine (NASEM) study on redesigning the process for establishing the Dietary Guidelines for Americans to guide its approach to using USDA’s food pattern modeling [...] Because this Committee’s report would consider birth to age 24 months as well as pregnancy and lactation, the need to apply food pattern modeling in a way that considered the needs of these unique phases of life was even more apparent. To accommodate this life-stage approach, the Committee used a new method in which the anticipated nutrient profiles were based on the proportions of foods consumed specific to each life stage, including children, adolescents, and younger, middle-aged and older adults. This chapter presents food patterns that apply to the U.S. population ages 2 years and older and Part D. Chapter 7: USDA Food Patterns for Children Younger than Age 24 Months presents, for the first time, food patterns that apply to the U.S. population from birth to age 24 months."

In light of this and other changes, this section addresses only one major question, but it's a doozy. Here it is...

"Are changes to the USDA Food Patterns needed based on the relationships identified in the systematic reviews? If so, how well do USDA Food Pattern variations meet nutrient recommendations for each stage of life? If nutrient needs are not met, is there evidence to support supplementation and/or consumption of fortified foods to meet nutrient adequacy?"

After a lengthy exploration, the Committee concludes, "The recommended USDA Food Patterns for Americans, which achieve healthy dietary intake and meet nutritional goals and energy balance, include the Healthy U.S.-Style, the Healthy Vegetarian, and the Healthy Mediterranean-Style Patterns. No additional food patterns were developed during the work of this Committee, confirming the guidance on Patterns issued from this and previous Committees (see Part D. Chapter 8: Dietary Patterns). Although these 3 Food Patterns have some key differences that allow for tailoring to individual preferences, they share some core components, including obtaining the majority of energy from plant-based foods, such as fruits, vegetables, legumes, whole grains, nuts and seeds, and obtaining protein and fats from nutrient-rich food sources, while limiting intakes of added sugars, solid fats, and sodium."

The use of food pattern modeling allows for a more insightful and varied approach to healthful eating, revealing behaviors that weren't as obvious before and offering a more complete picture of eating habits. For more details, check out pages 33 and 34 of this chapter.

And that brings us to the end of this section.

The next section of the guidelines is Future Directions, which you can read here. There are also lots of fascinating appendices to explore. But this does bring us to the end of our time with the scientific report from the 2020 Dietary Guidelines Advisory Committee. I hope you enjoyed it!

Remember, this is just an overview of the highlights. The report itself goes into FAR more detail, and you can read the whole thing here. It is now open for public comment, and there will be an online meeting on August 11 to discuss thoughts on the report.

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