Top Foods to Boost Your Immune System
- Polyphenols are immune system activators that help protect you from infections.
- Unfortunately, the typical American diet is low in these immune-boosting nutrients.
- Unhealthy diets, which don’t provide enough polyphenols, may increase COVID-19 infection risk and pose a greater risk to your health than risky sex, alcohol, drugs, and tobacco use combined.
- Learn about these miraculous molecules, where to find the richest sources of food polyphenols and how to incorporate them into your diet.
by Dr. John Neustadt
“Tell me what you eat and I will tell you what you are” is an unforgettable aphorism from the most famous book about food and cooking ever written: The Physiology of Taste, by Jean Anthelme Brillat-Savarin. Published in 1825, it’s loved by foodies around the world and has never gone out of print.1
Indeed, we are what we eat, and the foods you choose makes all the difference in your mental and physical health, vitality, and longevity. Yet many Americans are choosing foods that create inflammation, heart disease, Alzheimer’s disease, osteoporosis, arthritis, diabetes, depression, and cancer. In 2019 scientists from sixteen countries published an article in The Lancet, noting that “Unhealthy diets pose a greater risk to morbidity and mortality than does unsafe sex, and alcohol, drug, and tobacco use combined.” 2 And yet diets across the globe are inadequate in terms of nutrition, while overconsumption of unhealthy foods is on the rise.
Globally there are more people who are overweight than going hungry.3 Modern science and the global transportation system have revolutionized year-round access to food, and yet as a species, human beings are overfed and undernourished.4 We’re eating more calories, increasing from 2,016 to 2,390 calories per day5, but much of those calories are now high in sugars, fats, salt, and artificial ingredients that didn’t exist a century ago. We’re eating at restaurants or buying takeout half the time, and many of our meals are more like disguised desserts.6 Shockingly, 40% of Americans are obese7 and 10% suffer from diabetes.8
All of those unhealthy calories and chemicals weaken your immune system and the function of our cells.9 Refined sugar reduces the ability of white blood cells to destroy bacteria, and individuals with high blood sugar levels (prediabetic or diabetic) have are less able to fight infections and have increased inflammation.10,11 Omega-6 fatty acids, saturated fats, and trans-fats can create inflammation.12 Finally, our high salt diet can not only lead to high blood pressure, but it suppresses immune function, further increasing the risk of infection.13
These diets are rich in carbohydrates, proteins, and fats, but often poor in incredibly important micronutrients such as vitamins, minerals, flavonoids, and antioxidants. There are 40 essential minerals, vitamins, and other nutrients.14 Eminent researcher Bruce Ames, Ph.D., of UC Berkeley showed that deficiencies in micronutrients such as selenium, zinc, and copper create breaks in DNA and let free radicals go unchecked.15
The harmful impact of a calorie-rich but nutrient-poor diet is especially important now, during the COVId-19 pandemic, as preliminary research has shown that those suffering from obesity or type 2 diabetes are at increased risk for severe COVID-19 symptoms and mortality.16 Clearly, we can do a lot right now to increase our nutrient status, health, and immunity. And one of the most important things we can do is to eat a “rainbow” of fruits and vegetables, of every color, to increase our immunity by boosting our levels of polyphenols.
A diet that emphasizes fresh fruits and vegetables can slash your risk for heart disease, diabetes, high blood pressure, cancer, and gastrointestinal disease, reports the Harvard School of Public Health.17 One remarkable study followed over 70,000 women and nearly 38,000 men for 14 years. Astonishing as it may sound, those eating 8 or more servings of fruit and vegetables a day reduced the risk of heart attack and stroke by 30% percent—as compared to those only eating a paltry 1.5 servings a day. 18
These diets are rich in polyphenols, highly bioactive micronutrients packed with antioxidant power. Polyphenols are a category of nutrients that include isoflavones, lignans, flavonoids, anthocyanidins, terpenes, and various acids. Polyphenols can have a profound positive effect on your immune system and gut health.19 Polyphenols bind receptors on immune cells and help regulate your immune response. Polyphenols promote gut health and help maintain the mucosal layer that protects our intestinal lining. Polyphenols such as quercetin and luteolin, found in everything from celery to green papers, apples, and onions, are known to help regulate allergic responses.20 Polyphenols are even thought to be anti-cancer.21
One famous health-promoting diet high in polyphenols is the Mediterranean diet—originally consumed by Italians and Greeks and rich in olives and olive oil, vegetables such as tomatoes, and moderate amounts of red wine.22 Another famous longevity diet also packed with polyphenols is the traditional diet of the Okinawans, who live on a group of islands in the Pacific, and boast many individuals who live to 100 years or more. The Okinawan diet contains about seven servings of vegetables and one or two servings of grain per day. It’s rich in botanicals like turmeric and bitter melon and a staple is the purple sweet potato, high in flavonoids called anthocyanins that give the potato its violet color.23 These healthy diets have one thing in common. They are essentially a whole foods diet that is rich in alkaline foods.
We may not live in the Mediterranean or the Pacific islands, but the wide array of fruits and vegetables available to us today at any supermarket or farmer’s market offers many healthy flavonoids and antioxidants.24
Since different foods are rich in so many different polyphenols, it’s a good idea to eat a wide variety of fruits and vegetables every day—as all the colors and types signal different flavonoid and polyphenol content. You might want to start your day by creating a fruit salad to nosh from all day long, slicing up an array of delicious fruits of many hues—red, blue and blackberries, orange and yellow citrus, mango, papaya, green and purple grapes, pineapple and green kiwis. Or you may want to make a fruit and veggie smoothie. Throw together a delicious greens salad that will last a few days—including a variety of lettuce types, watercress, arugula, parsley, cilantro, carrots, peppers of all colors, olives, and a dressing that includes extra virgin olive oil along with lemon or vinegar. For veggies, keep in mind the potent health-promoting cruciferous vegetable family, which includes broccoli, cauliflower, brussels sprouts, and others, as well as immune-boosting mushrooms, garlic and onions.25 Don’t forget green tea, either, with its potent polyphenol, epigallocatechin-3-gallate (EGCG), known to reduce inflammation and protect cells from damage.26
To help you maximize your daily consumption of polyphenols, listed below are the richest sources of these important micronutrients. These are drawn from a list of the 100 richest dietary sources of polyphenols.27 In general, spices are highest in polyphenols, so use them liberally, followed by fruits, seeds, vegetables, and more.
Foods are listed in order of their polyphenol content, from the most polyphenols to the least in each category.
Cocoa (also called cacao) products come from the seeds of the cocoa tree (Theobroma cacao), which are used to make chocolate. The purer the chocolate, the greater the polyphenols.
Coffee and Tea
Herbs and Spices
Seeds and Nuts
1 Brillat-Savarin JA. The Physiology of Taste. 1825. [Report]
2 Willett W, Rockström J, Loken B, et al. Food in the Anthropocene: the EAT-Lancet Commission on healthy diets from sustainable food systems. Lancet. 2019;393(10170):447-492. [Article]
3 World Disasters Report 2011, Focus on Hunger and Malnutrition. Geneva: International Federation of Red Cross and Red Crescent Societies; 2011: 16. [Report]
4 Cronise RJ, Sinclair DA, Bremer AA. The “metabolic winter” hypothesis: a cause of the current epidemics of obesity and cardiometabolic disease. Metab Syndr Relat Disord. 2014;12(7):355-361. [Article]
5Bentley J. U.S. Trends in Food Availability and a Dietary Assessment of Loss-Adjusted Food Availability, 1970-2014. [Report]
6 Impact Lab. It’s Easy to Become Obese in America. Aug 2018. [Report]
7CDC. Adult Obesity Facts. June 2020. [Report]
8 CDC. National Diabetes Statistics Report. 2020. [Report]
9 Myles IA. Fast food fever: reviewing the impacts of the Western diet on immunity. Nutr J. 2014;13:61. [Article]
10Sanchez A, Reeser JL, Lau HS, et al. Role of sugars in human neutrophilic phagocytosis. Am J Clin Nutr. 1973;26(11):1180-1184. [Article]
11Shodja MM, Knutsen R, Cao J, et al. Effects of glycosylated hemoglobin levels on neutrophilic phagocytic functions. Jacobs J Diabetes Endocrinol. 2017;8(2):9-16. [Article]
12Calder PC. Fatty acids and immune function: relevance to inflammatory bowel diseases. Int Rev Immunol 2009, 28:506–534 [Article]
13Jobin K, Stumpf NE, Schwab S, et al. A high-salt diet compromises antibacterial neutrophil responses through hormonal perturbation. Sci Transl Med. 2020;12(536):eaay3850. [Article]
14Ames, Bruce N. Low micronutrient intake may accelerate the degenerative diseases of aging through allocation of scarce micronutrients by triage. PNAS 2006;103(47)17589 –17594. [Article]
15Ames BN. DNA damage from micronutrient deficiencies is likely to be a major cause of cancer. Mutation research. 2001;475(1-2):7-20. [Article]
16Butler MJ, Barrientos RM. The impact of nutrition on COVID-19 susceptibility and long-term consequences. Brain Behav Immun. 2020;87:53-54. [Article]
17Harvard School of Public Health. Vegetables and Fruits. [Report]
18Schwingshackl L, Schwedhelm C, et al. Food groups and risk of all-cause mortality: a systematic review and meta-analysis of prospective studies, Am J Clin Nutr. 2017 Jun;105(6):1462-1473. [Article]
19Dalgaard F, Bondonno NP, Murray K, et al. Associations between habitual flavonoid intake and hospital admissions for atherosclerotic cardiovascular disease: a prospective cohort study [published correction appears in Lancet Planet Health. 2019 Dec;3(12):e499]. Lancet Planet Health. 2019;3(11):e450-e459 [Article]
20 Shaik Y, Caraffa A. Impact of polyphenols on mast cells with special emphasis on the effect of quercetin and luteolin. Cent Eur J mmunol. 2018;43(4):476-481 [Article]
21Ding S, Jiang H, Fang J. Regulation of immune function by polyphenols. J Immunol Res. 2018;2018:1264074 [Article]
22Martínez-González MA, Salas-Salvadó J, Estruch R, et al. Benefits of the Mediterranean Diet: Insights from the PREDIMED study. Prog Cardiovasc Dis. 2015;58(1):50-60. [Article]
23Beuttner D. Why Japan’s longest-lived women hold the key to better health. Dec 2017. [Report]
24Ding S, Jiang H, Fang J. Regulation of Immune Function by Polyphenols. J Immunol Res. 2018;2018:1264074. [Article]
25Kapusta-Duch J, Kopeć A, Piatkowska E, Borczak B, Leszczyńska T. The beneficial effects of Brassica vegetables on human health. Rocz Panstw Zakl Hig. 2012;63(4):389-395. [Article]
26Afzal M, Safer AM, Menon M. Green tea polyphenols and their potential role in health and disease. Inflammopharmacology. 2015;23(4):151-161 [Article]
27Pérez-Jiménez J, Neveu V, Vos F et al. Identification of the 100 richest dietary sources of polyphenols: an application of the Phenol-Explorer database. Eur J Clin Nutr. 2010;64 Suppl 3:S112-S120. [Article]
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