October 2021 Issue
CPE Monthly: Functional Foods’ Role in Chronic Disease Prevention
By Natalie Sexton, MS, RDN, CSR, LD
Vol. 23, No. 8, P. 50
Suggested CDR Performance Indicators: 8.1.4, 8.1.5, 10.4.4, 10.4.5
CPE Level 2
Six in 10 adults in the United States are living with at least one chronic disease, and 4 in 10 American adults have two or more chronic diseases.1,2
To be considered a chronic disease, a condition must be ongoing for at least one year; it also must require consistent medical care, restrict activities of daily living, or both.2 Heart disease, cancer, and diabetes are the most common chronic diseases in the United States, and COPD, Alzheimer’s disease (AD), and chronic kidney disease also are prevalent.
While it’s well known dietary patterns influence chronic disease risk, researchers are examining the effects that individual foods may have on health. These individual foods, often referred to as “functional foods,” frequently are promoted as having the ability to prevent chronic disease when included daily in a person’s diet.
This continuing education course reviews functional foods and their potential role in chronic disease prevention and provides recommendations RDs can make to clients.
Classifying Functional Foods
The nutrients in most foods can be considered functional. Protein aids in muscle repair, carbohydrates and fats provide energy, and vitamins and minerals help with cell function.3 However, labeling foods as “functional foods” first began in Japan in the 1980s.4 The term has grown to apply to foods, both conventional and modified, that have added components meant to confer physiological benefits beyond basic nutrition.3 Examples of conventional functional foods include fruits, vegetables, whole grains, legumes, and nuts, while modified functional foods can include fortified juices and fortified cereals.3,4
Health professionals have long been encouraging Americans to include functional foods in their everyday diets to avoid nutrient deficiencies and support growth and development. However, functional foods have experienced a surge in popularity for their potential ability to protect against chronic disease. As the incidence of chronic disease and health care costs continue to rise, consumer and food industry interest in functional foods also is increasing.5 Sales of functional or fortified foods reached $247 billion worldwide in 2017, with the United States having the largest functional food market.6
Regulation of Functional Foods
The FDA doesn’t provide a legal or universally accepted definition of functional foods, so no standardized or regulatory guidelines regarding use of functional foods exist.5,7 However, the FDA does control the health claims used on food labels.3 A health claim describes the relationship between a food, food component, or dietary ingredient with a disease or health-related condition.7 Food companies are prohibited from using health claims on food labels without FDA approval. Some health claims, such as the heart health claims for plant sterols and stanols, have been FDA approved for use on food labels.5
Heart disease is the leading cause of death from chronic disease in US adults, killing about 655,000 Americans each year.8 A variety of produce, high-fiber foods, and sources of unsaturated fats can impact the onset of heart disease.
Fruits and Vegetables
A systematic review of 95 studies showed an inverse association between fruit and vegetable consumption, up to 800 g/day, and heart disease risk. These studies included apples, pears, citrus fruits, cruciferous and green leafy vegetables, and salads.9
Flavonoids are plant-based phytochemicals with antioxidant or anti-inflammatory activity and have the ability to reduce LDL cholesterol oxidation. A large prospective cohort study found that US adults with the highest flavonoid intake, ≥359.7 mg/day, exhibited a significantly lower risk of death from heart disease. Even small amounts of flavonoid consumption were inversely associated with heart disease risk. Fruits with >50 mg/100 g of flavonoids include apples, blueberries, grapes, oranges, grapefruits and grapefruit juice, pears, and strawberries. Other significant sources include mixed nuts, walnuts, black and herbal teas, chocolate, red wine, and garlic powder.10
Anthocyanins, a class of flavonoids found in berries, also have been shown to reduce blood pressure and heart disease risk. One epidemiologic study of 60 postmenopausal women found that those who consumed at least two servings of strawberries per week had a significantly lower CVD risk compared with those who didn’t consume strawberries.11
The high monounsaturated fatty acid content of olive oil, as well as its other constituents—tocopherols and polyphenols—give it antioxidant, anti-inflammatory, and vasodilatory properties that contribute to cardiovascular health. Olive oil has been found to lower the frequency of myocardial infarction, stroke, and other cardiovascular events.12
In an observational study of 99,379 participants, daily consumption of more than one-half tablespoon of olive oil was associated with a 15% lower risk of CVD and a 21% reduced risk of coronary heart disease. Olive oil also showed significant health benefits compared with butter and margarine. Substituting one teaspoon of olive oil for the same amount of butter, trans fat–containing margarine, mayonnaise, or dairy fat decreased CVD and coronary heart disease risks by 5% and 7%, respectively.13
The consumption of plant sterols, also referred to as phytosterols, can block cholesterol absorption in the small intestine and lower total and LDL cholesterol levels.14 Phytosterols are found naturally in minimal quantities in foods such as fruits, nuts, and seeds. However, this is far below the recommended effective cardioprotective dose of 2 to 3 g/day.15 Consuming two to four tablespoons of phytosterol-enriched margarine can provide the recommended daily dose of phytosterols.16
Still, studies show an unclear relationship between phytosterols and cardiovascular risk.14 Therefore, phytosterol-enriched margarine or other foods are best recommended as an adjunct to a heart-healthy lifestyle and, if indicated, lipid-lowering medication.15
Legumes and Nuts
Soybean isoflavones may improve arterial elasticity, enhance blood pressure reduction, lower serum cholesterol, and decrease lipid oxidation. Soybean protein upregulates LDL receptor levels in the liver, increasing LDL metabolism and decreasing plasma LDL concentration, resulting in a possible 6% to 12% reduction in total plasma cholesterol. Soybean protein also causes increased expression of an antioxidant enzyme, superoxide dismutase.11
Despite some confusion on the part of consumers regarding the interaction between soy intake and estrogen receptors, the FDA and American Heart Association encourage soy consumption.11,17,18 The FDA approves health claims stating that intake of “25 g of soy protein a day, as part of a diet low in saturated fat and cholesterol, may reduce the risk of heart disease.”18
Further research supports diets rich in high-quality plant protein sources, such as beans and nuts, to lower total and LDL cholesterol levels. Data from 36 studies showed favorable changes in total and LDL cholesterol levels when red meat was substituted with soy protein or soy products, walnuts, tree nuts, almonds, beans, lentils, or peas.19
Nuts have been shown to lower LDL and triglyceride levels. Their high vitamin E and L-arginine content may improve artery health, reduce plaque buildup, and decrease risk of blood clots. Their high omega-3 fatty acid content may lower inflammation levels.20 Nuts also are rich in unsaturated fats, fiber, and plant sterols, all of which have demonstrated heart health properties. The 2020–2025 Dietary Guidelines for Americans recommend including unsalted nuts or nut butter in the diet to meet the recommended consumption of 5 oz of nuts, seeds, or soy products each week.21
Omega-3 Fatty Acids
Eating at least two servings, or 8 oz, of omega-3–rich fish each week can lower heart disease risk by reducing inflammation, triglycerides, blood pressure, blood clotting, and irregular heartbeat. Omega-3 fatty acids also can decrease risk of stroke and heart failure. Fish rich in omega-3s include salmon, canned light tuna, sardines, cod, herring, lake trout, and Atlantic mackerel. Eating fish or other omega-3–rich food sources such as flaxseeds and flaxseed oil, walnuts, canola oil, soybeans and soybean oil, and chia seeds appears to provide greater heart health benefits than supplementation with omega-3 fatty acids.22 Foods such as pasta, cereal, eggs, tofu, and dairy products may be fortified with omega-3 fatty acids, but amounts and types vary among products.
Whole grains have been shown to lower risk of coronary heart disease, stroke, and CVD. Whole grains tend to be good sources of fiber, B vitamins, iron, magnesium, and zinc. The main sources of whole grains in the US food supply are whole grain breads and breakfast cereals.23
Although the amount that provides the most heart health benefits is unclear, an analysis of 45 studies showed that an intake of as much as 210 to 225 g/day (seven to 7.5 servings) of whole grains can significantly reduce CVD risk. The whole grains in this study included whole grain bread, whole grain breakfast cereals, and added bran.23
Tea and Coffee
Tea, especially green tea, has been shown to slow the age-related decline of HDL cholesterol. In a six-year study of more than 80,000 Chinese adults, drinking tea at least four times per week was associated with an 8% reduction in cardiovascular risk compared with consuming tea less than once per month. Green tea showed a slightly stronger effect than black tea.24
Consumption of black coffee, whether caffeinated or decaf, is associated with lower risk of death attributed to heart disease.25 While coffee contains significant numbers of antioxidants, it also contains cafestol, a compound that has been shown to increase LDL cholesterol. However, using paper filters when brewing will remove the cafestol.26
Cancer is the second-leading cause of death from chronic disease in the United States, killing about 600,000 Americans each year, with more than 1.6 million people newly diagnosed each year.27 Many plant-based foods, coffee, tea, and even some dairy products have shown potential for decreasing cancer risk.
Fruits and Vegetables
People who consume fruit- and vegetable-rich diets have a lower risk of many different types of cancer.28 Fruits and vegetables contain high levels of polyphenols that show antioxidant properties. Ellagic acid, a common plant polyphenol, prevents carcinogenesis by reducing the DNA-binding ability of carcinogens. Ellagic acid is abundantly found in strawberries, raspberries, black currants, grapes, and other fruits. Cherries also have shown strong anticancer effects. In vitro studies have found that the combination of vitamin C and raspberry fruit extract kills stomach, colon, pancreatic, and breast cancer cell lines.11
A systematic review showed an inverse association between the intake of green-yellow vegetables and cruciferous vegetables, up to 600 g/day, and cancer risk.9 The National Cancer Institute emphasizes dark green and orange vegetables and legumes in its current cancer prevention recommendations and advises daily consumption of one to 2.5 cups of fruits and one to four cups of vegetables, depending on individual energy needs.28
Legumes and Nuts
Research suggests that soybean isoflavones are protective against certain types of cancer. The lower rate of breast and prostate cancer in China and Japan compared with Western countries has been attributed to the higher soyfood consumption in those countries, especially during development or early life.11 Although some research contradicts the chemoprotective properties of soybeans, the American Cancer Society considers soyfoods healthful and safe.29
Overall, research remains mixed regarding dairy and cancer risk, especially gastric cancer.30-32 Some studies show that high intake of dairy foods may increase risk of prostate cancer but decrease risk of breast and colorectal cancer.33-35 According to extensive review by the World Cancer Research Fund/American Institute for Cancer Research Expert Panel as part of the organizations’ Continuous Update Project on cancer prevention, “strong evidence” exists showing that consumption of dairy foods reduces colorectal cancer risk.36 Whey proteins in milk may act as potential anticarcinogenic agents. The cysteine and other sulfur-containing amino acids may enhance immune response and antioxidant synthesis.11
Fermented milk products such as yogurt contain probiotics that play a role in digestive and immune system health. Clinical trials show that the Lactobacillus casei strain Shirota, a probiotic bacteria strain, inhibited tumor growth and migration in human malignant cells. Probiotic bacteria also play a role in metabolizing other compounds such as isoflavones, flavonoids, and polyphenols.11
While much research supports the inverse association between whole grain intake and risk of colorectal cancer, several studies also connect whole grain intake with a reduced risk of total cancer.23 The short-chain fatty acids formed from fiber fermentation in the colon inhibit carcinogenesis, enhance pathogen destruction, and increase removal of ammonia and other toxins. The phenolics and phytoestrogens in whole grains act as antioxidants in the body.11 Still, questions remain about the amount of whole grains needed to provide optimal cancer risk reduction benefits.23
Coffee and Tea
Polyphenols in green and black teas have antioxidant activity that also may help prevent cancer.37 Moreover, tea polyphenols can inhibit tumor cell proliferation and stimulate apoptosis of cancer cells.11,37 While strong evidence supports the anticarcinogenic effects of tea, especially green tea, inconsistencies in results may be attributed to variables in tea preparation, amount consumed, and other lifestyle factors.37
More than 34 million Americans have diabetes, but 1 in 4 don’t know they have it. Likewise, more than 88 million Americans have prediabetes, but 90% are unaware.38 Diabetes increases the risk of other chronic diseases such as heart and kidney disease.
Fruits and Vegetables
Higher fruit or green leafy vegetable intake can decrease diabetes risk.39 Apples, apricots, grapes, peaches, pears, and plums also have been linked to lower diabetes risk. Blueberries, which have received much notoriety as a functional food, also were shown to be beneficial in preventing diabetes.40 A double-blinded, randomized controlled trial involving 52 men with type 2 diabetes investigated the effect of blueberries on cardiometabolic parameters. Participants consumed either 11 g of freeze-dried blueberries or 11 g of placebo with their morning and evening meals (for a total of 22 g/day) for eight weeks but otherwise continued their typical diet. Average hemoglobin A1c, fructosamine, triglycerides, aspartate transaminase, and alanine transaminase levels were significantly decreased for those consuming blueberries compared with those in the placebo group. No significant improvements were observed in fasting plasma glucose and serum insulin levels.41
The antioxidants, anthocyanins, and anthocyanidins in cherries may prevent diabetes by reducing oxidative stress and enhancing insulin production. Their high fiber content and lower glycemic index also may improve glucose utilization.11 Other berries, such as strawberries, cranberries, raspberries, and blueberries, contain the same potential antidiabetes properties.42
Green leafy vegetables provide relatively few calories and carbohydrates per serving. Consuming high volumes of these foods can help increase satiety and provide a bounty of nutrients without drastically affecting blood sugar or causing weight gain. Cruciferous vegetables also have been linked to lower risk of prediabetes.43
Soy proteins have shown weight loss effects by increasing satiety and thereby reducing overall caloric intake and postprandial plasma insulin levels.11 Other legumes also provide protection against type 2 diabetes. The PREDIMED study found that consuming 28.75 g/day (equivalent to 3.35 servings/week) of lentils, chickpeas, beans, and peas lowered diabetes risk by 35% compared with only 12.73 g/day, or 1.5 servings per week. Specifically, participants who consumed a higher amount of lentils (almost one serving/week) had a 33% lower risk of diabetes. In addition, the study found that replacing half a serving of eggs, bread, rice, or baked potato with an equivalent amount of legumes each day lowered type 2 diabetes risk.44
Studies consistently show that high dietary fiber intake (>25 g/day in women and >38 g/day in men) can assist with blood sugar management and reduce type 2 diabetes risk by 20% to 30%.3,45 Many studies found high-fiber cereals to be superior to high-fiber fruits and vegetables in improving insulin resistance and diabetes risk.45
Coffee and Tea
Numerous studies have connected regular coffee consumption with a lower risk of insulin resistance and type 2 diabetes. Prospective studies of a total of 1,663,319 people from three cohorts found that those who increased their daily coffee intake by more than one cup over four years experienced a 12% decrease in their type 2 diabetes risk. But a greater than one-cup decrease in daily coffee intake was associated with a 17% higher type 2 diabetes risk.46
Black, green, and oolong teas have shown similar antidiabetes effects as coffee.47 These teas, all harvested from the Camellia sinensis plant, contain polyphenols, which may improve insulin sensitivity. Studies primarily focus on green and black tea, but oolong, chamomile, rooibos, and ginger tea also have health benefits (though herbal teas such as chamomile, rooibos, and ginger aren’t true “teas” in that they don’t come from the C sinensis plant). However, adding milk to tea decreased the antidiabetes effects.
COPD, a type of chronic lower respiratory disease, is the third-leading cause of death from chronic disease in the United States, with almost 15.7 million Americans reporting having COPD and many more undiagnosed.48 Fruits, vegetables, and whole grains have been found to be beneficial, especially for current or former smokers who have an increased risk of COPD.
Fruits and Vegetables
Smoking is a notorious risk factor for COPD, but two large population studies found that high long-term consumption of fruits and vegetables significantly reduced the risk of COPD among current and ex-smokers.49,50 Although inconsistent, research suggests fruits and vegetables still can decrease COPD risk regardless of smoking habit. A meta-analysis of eight studies found an inverse association between fruit and vegetable intake and COPD risk. Overall fruit intake may reduce the risk of COPD by 28%; apples and pears showed an inverse association, while bananas and citrus fruits did not.51
Two studies in the meta-analysis provided specific vegetable types (green leafy vegetables, cruciferous vegetables, and root vegetables) that may reduce risk but showed no statistically significant results. Three studies showed vegetable intake to be beneficial only in smokers. But, overall, the data indicated that vegetable intake may reduce COPD risk by 24%.51
Due to its anti-inflammatory properties, dietary fiber from whole grains has been suggested to decrease risk of COPD and other respiratory diseases.22,52 A study involving 45,058 men found that a total daily fiber intake of ≥36.8 g vs <23.7 g showed a strong inverse association with COPD incidence in current or former smokers. However, no significant association was found in never smokers.52
Coffee, Tea, and Alcohol
Green tea is thought to reduce COPD risk through its antioxidant and anti-inflammatory effects. A Korean study involving 13,570 participants showed that increasing the frequency of green tea intake from never to two or more times per day decreased COPD incidence from 14.1% to 5.9%, respectively.53
Even moderate consumption of beer and wine may decrease COPD risk. A prospective cohort study of 44,254 Swedish men found that those who consumed beer or wine in moderation had the lowest risk of COPD.54
In 2020, approximately 5.8 million Americans had AD, the most common form of dementia. Although no single cause has been identified for AD, researchers are discovering evidence that suggests the same healthful behaviors encouraged to prevent heart disease, diabetes, and cancer also may help prevent AD.55
Fruits and Vegetables
The MIND (Mediterranean-DASH Intervention for Neurodegenerative Delay) diet, a variation of the Mediterranean diet, incorporates the blood pressure–lowering benefits of the DASH (Dietary Approaches to Stop Hypertension) diet to prevent AD. The diet focuses on plant-based foods, encouraging at least six servings per week of green leafy vegetables, at least one serving per day of other vegetables, and two or more servings per week of berries. One study found that a daily serving of green leafy vegetables was associated with slower age-related cognitive decline.56 Berry consumption, specifically blueberries, has been reported to improve cognitive function.11
A recent study by the National Institutes of Health found that fish was the most important food to lower both risk of cognitive impairment and cognitive decline.57 The omega-3 fatty acids found in fish have been shown to lessen cognitive decline, dementia, and AD. One epidemiologic study showed that Dutch adults who consumed >20 g of fish per day had a lower risk of AD dementia and cognitive decline. A four-year study of US older adults with normal brain function found that those who consumed fatty fish at least once per week had a 60% lower risk of AD.11 The MIND diet recommends at least one serving of fish per week.56
Coffee, Tea, and Alcohol
Caffeine intake has been linked to a lower risk of AD.25 While tea and coffee are significant sources of caffeine, they also contain certain compounds found to reduce the risk of AD. Epigallocatechin gallate, a polyphenol found in tea leaves, can inhibit the collection of amyloid-beta plaques in the brain, a major cause of AD. Trigonelline, an alkaloid found in coffee, can promote regeneration of brain neurons. The antioxidant properties of coffee also can prevent brain tissue degeneration by decreasing brain tissue–damaging free radicals.11
Daily moderate alcohol consumption also appears to be beneficial, with red wine showing additionally protective effects against cognitive decline.58 The MIND diet recommends no more than one glass per day of wine.56
Kidney disease is the ninth-leading cause of death from chronic disease in US adults, and 6 million American adults have diagnosed kidney disease.59 Functional foods indirectly can avert kidney disease by preventing its major risk factors: diabetes, high blood pressure, and heart disease.60
Legumes and Soy Products
The Academy of Nutrition and Dietetics supports the use of vegetarian diets for the prevention and treatment of chronic diseases. Evidence supports that those who follow an appropriately planned vegetarian or vegan diet are at a lower risk of heart disease, hypertension, and type 2 diabetes—three major risk factors for chronic kidney disease (CKD). Regular consumption of legumes and soy products will provide adequate protein and essential amino acids in the vegetarian diet.61
Dietary soybean protein decreases kidney disease risk by reducing the risk of diabetes, hypertension, and hypercholesterolemia. In patients with type 2 diabetes and nephropathy, substituting 50% of dietary animal protein intake with soybean protein resulted in significant improvements in kidney function and lipid profiles. Soy protein–supplemented diets also have been shown to curb the progression of polycystic kidney disease.11
Coffee and Alcohol
Research suggests that daily coffee intake may prevent CKD. A study involving 8,717 participants found that those who drank one cup per day or two or more cups per day had lower rates of kidney function decline than those who drank no coffee, less than one cup per week, or one to six cups per week.62
One study suggests that moderate wine consumption (less than one glass per day) can decrease CKD risk. Participants who drank less than one glass of wine per day had a 37% lower occurrence of CKD than those who drank no wine.63
Future of Functional Foods
In 2017, nearly two-thirds of US adults stated that healthfulness, with a specific focus on a food product’s benefits, significantly impacted their food and beverage purchases over the past year. Foods and beverages with added vitamins or minerals were the top focus.6
With little to no regulation regarding functional food use, the need for thorough scientific evidence regarding functional food health claims is crucial. The goal isn’t to identify and evaluate only the benefits of functional foods, but also to compare the effects of whole foods vs individual nutrients. Although current evidence leans toward conventional functional foods for disease-preventing benefits, the food industry continues to focus primarily on the creation and promotion of modified functional foods.5
Putting It Into Practice
Despite functional foods being strongly linked with some health benefits, health professionals still should take a comprehensive approach toward chronic disease prevention and management. Simply adding functional foods or supplements into a person’s daily diet is unlikely to outweigh the effects of fewer healthful diet or lifestyle choices and other risk factors contributing to disease. Functional foods, when combined with healthful eating patterns and lifestyle choices, may significantly reduce the risk of chronic disease.
Dietitians should educate their clients on how to properly incorporate functional foods into their diet and address any barriers, real or perceived, to consuming these foods. In addition to using evidence-based guidelines to dispel the multitude of diet misinformation, dietitians can help clients find ways to incorporate functional foods into their daily diets.
— Natalie Sexton, MS, RDN, CSR, LD, is a registered dietitian, health coach, and freelance writer based in Longview, Texas.
After completing this continuing education course, nutrition professionals should be better able to:
1. Discuss the prevalence of chronic disease among US adults.
2. Educate clients on the role of functional foods in chronic disease prevention.
3. Choose specific functional foods that could be beneficial for reducing risk of chronic disease.
4. Develop specific dietary recommendations to help clients incorporate functional foods appropriately into their daily diets.
CPE Monthly Examination
1. According to this course, what is the second-leading cause of death from chronic disease in the United States?
b. Heart disease
d. Chronic kidney disease
2. According to this course, what is the main source of whole grains in the US food supply?
a. Brown rice and whole wheat pasta
b. Oats and quinoa
c. Corn and popcorn
d. Whole grain breads and breakfast cereals
3. What compound in coffee has been shown to increase LDL cholesterol?
b. Chlorogenic acid
d. Quinic acid
4. What’s the recommended effective cardioprotective dose of plant phytosterols?
a. 1 to 2 g/day
b. 2 to 3 g/day
c. 3 to 4 g/day
d. 4 to 5 g/day
5. Sales of functional foods reached what amount worldwide in 2017?
a. $135 billion
b. $247 billion
c. $316 billion
d. $450 billion
6. Of the “teas” mentioned in this course, which of the following comes from the Camellia sinensis plant?
7. How many cups of fruit does the National Cancer Institute recommend eating each day?
a. One to 2.5
b. One to 3.5
c. One to four
d. One to five
8. How many Americans have prediabetes?
a. >58 million
b. >64 million
c. >72 million
d. >88 million
9. How many Americans had Alzheimer’s disease in 2020?
a. 1.6 million
b. 5.8 million
c. 6 million
d. 9 million
10. According to this course, which category of vegetables has been associated with a lower risk of prediabetes?
a. Green leafy
b. Legumes (beans and peas)
c. Dark yellow
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