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Stress, inflammation and diet

By Daniel Clarke ANutr, Senior Nutrition Executive

The basics

If you’ve read our article what is stress? you’ll know that stress, in its most basic sense, is the body reacting to a change (a stressor) that requires a response. When stress is applied in the context of diets, the conversation is around the body’s response to certain foods. This could mean these foods are directly causing a response or they’re modulating the body’s reaction to stressors, such as ageing or smoking.

Stress activates the immune system and part of that activation involves inflammation. There are many different components of the immune system that form part of the inflammatory response and they, in turn, release a whole host of inflammatory substances, such as cytokines and hormones that other cells in the body respond to.

Why does inflammation occur?

Inflammation can occur due to an infection, injury or may have a less obvious cause[1]. There are several visible signs of inflammation, such as swelling, redness or soreness, but often, there may be no signs present[2].

Acute vs chronic inflammation

Inflammation that occurs over a relatively short amount of time is called acute inflammation, whereas chronic inflammation can continue for years, or even indefinitely[2]. Chronic inflammation can carry on when the cause remains unresolved, repeatedly occurs or the consequences continue unchecked[1]. Inflammation can also be classified as localised (happening in a specific place) or systemic (affecting several different areas of the body).

Due to the effects of inflammation, the longer it carries on, the more likely there are to be adverse consequences[3]. This is one reason why chronic inflammation is seen in such a negative light and has gained more attention in recent years.

Measuring inflammation

Although there are visible signs of inflammation, a person may be asymptomatic, especially in the early stages of chronic inflammation[2]. The good news is inflammation can be measured through specific markers even if symptoms are not present. The most well-known and commonly used inflammatory marker is C-reactive protein (CRP)[4]. CRP is produced by the liver in response to the cytokines released by the cells of the immune system[5]. As CRP only hangs around for a short amount of time and levels are mainly determined by how much is produced, it’s a really good indicator of inflammation[6].

Cytokines such as interleukin-6 (IL-6) and tumour necrosis factor-alpha (TNF-α) can also be used as markers in their own right, or alongside CRP[7-9]. In scientific studies, the control group usually has cytokines in the blood present in low levels, so elevated levels may indicate an inflammatory response[10].

Unfortunately, you can’t measure inflammation at home, but these tests can be prescribed by your doctor if they feel the results can provide an insight into your wellbeing.

How does this all link to what we eat?

There are many diseases that concern chronic inflammation, and several relate to what we eat. Two examples to illustrate this include; coeliac disease which is a direct result of the body’s immune system reacting to a protein found in wheat, rye and barley called gluten[11] and rheumatoid arthritis which can be affected by the diet, for better or for worse [12]. So, diet can influence inflammation in certain disease states, but what about in healthy individuals?

Anti-inflammatory diets concept

The fundamental idea behind diets that fall under the anti-inflammatory diet umbrella is that certain foods increase inflammation and others decrease it. So an anti-inflammatory diet reduces, or cuts out, foods that exacerbate inflammation while being rich in foods that are thought to be anti-inflammatory[13].

Using the WorldCat search engine, there were just under 300 books listed for “anti-inflammatory diet” in 2010[13]. There are now over 700[14]. The idea of connecting inflammation, health and diet to one another has exploded in recent years. This is possibly because it appeals to our sense of logic while also sounding scientific.

What makes up an anti-inflammatory diet?

The diets touted by these books can vary significantly as there is no single anti-inflammatory diet or defined rules. Some suggest a balanced varied diet, in line with government recommendations, and others advise cutting out entire food groups such as grains, soy and dairy. The issue with eliminating foods is, without proper thought, intake of certain nutrients may become inadequate. On the other hand, foods that are often recommended for an anti-inflammatory diet are oily fish, nuts, berries, green leafy vegetables, olive oil and spices[15].

The dietary inflammatory index

Diet certainly can affect inflammatory markers and the risk of developing diseases with an inflammatory element[16, 17]. Whether the foods eaten are reducing disease risk through anti-inflammatory mechanisms is uncertain, but it’s clear inflammation is only part of the puzzle[18, 19].

The dietary inflammatory index was produced in 2009[20] to provide a score of the inflammatory effect of different nutrients. It was later refined in 2014 with an improved scoring system and by including data from global populations[21]. The index was based on over 1,900 studies that consisted of cell culture, animal and human trials which investigated the effect of 45 food elements on inflammatory markers, including CRP, IL-6 and TNF-α. The elements consisted of nutrients, herbs and spices. An important note is the overall score considered the whole diet, not just individual foods or nutrients.

The findings

What this research found is that omega-3 fatty acids and phytonutrients were associated with a low inflammatory index[21]. This translates to eating foods high in omega-3 fatty acids, like oily fish, flaxseed and walnuts, along with the many different phytonutrients found in plant foods such as non-starchy vegetables and fruits of various colours.

Contrary to this, diets high in calories, refined carbohydrates, sugar and saturated fat were more likely to be pro-inflammatory[21].

The average Western diet lacks everything from the first paragraph and is high in everything from the second, while the Mediterranean diet is the opposite. Studies investigating both these diets and their effect on inflammation support the findings from the dietary inflammatory index [22-24].

The disclaimer

The context of the whole diet, what people eat day in, day out for long periods of time, is really important. In other words, we’re not saying that eating a handful of blueberries every day makes inflammation disappear or that saturated fat is bad because it’s inflammatory.

Lots of studies administer super-high amounts of an isolated compound to cells or rats, at levels that could never be achieved through diet alone[25, 26]. Alternatively, when the same compound is looked at in humans we see little effect, if any[25, 26]. This is because dietary research in humans isn’t easy. For example, a food may be seen as anti-inflammatory because it’s being eaten instead of another food or because it’s often eaten with other foods. Moreover, the biological system of the human body is more complex than single cells or rats further complicating results between such studies.

Marketing hype

Inflammation has become a buzzword and catch-all term for the cause of all diseases, and it’s then linked to a food or diet as a reason to sell you something. But remember, it’s not that simple. As previously mentioned, isolating compounds shown to have an effect in cells, such as antioxidants, doesn’t mean the same effect will be seen in humans[27, 28]. In fact, the opposite outcome can occur as antioxidants given during exercise may impact the benefits exercise provides[29].

Considering the magnitude of an effect is also important. How much food or nutrients are anti-inflammatory, such as fish oil, is often greatly exaggerated by marketers. Fish oil has been shown to possibly have an anti-inflammatory effect, but this effect is relatively small, especially at dietary doses[30].

Likewise, claiming a particular diet is “the best” because it excludes certain food groups based on inflammation is also a red flag. Trying to pinpoint specific nutrients in healthy diets and stating their effect on inflammation isn’t constructive. A diet is the sum of all its parts.

The takeaways

For most people, the evidence around inflammation leads to the same foods we’ve been told to eat for years, i.e. fruits, vegetables, whole grains and oily fish, while limiting the overconsumption of calories, saturated fat and refined carbohydrates[15, 21]. A plant-based diet is one way to achieve this, which Huel can form a part of.

If you see other places on the internet say “do this because of inflammation”, it’s usually a good sign to take what they’re saying with a pinch of salt (the anti-inflammatory kind, of course) and use the time you would have spent reading their spiel to relax. Go on a walk, make a hot drink, listen to some music. It will save you your sanity and probably some money too.

References

  1. Pahwa R, et al. Chronic Inflammation. StatPearls Publishing: Treasure Island, Florida; 2020.
  2. InformedHealth.org. What is an inflammation? Institute for Quality and Efficiency in Health Care: Cologne, Germany; 2010.
  3. Furman D, et al. Chronic inflammation in the etiology of disease across the life span. Nat Med. 2019; 25(12):1822-32.
  4. Luan Y-Y, et al. The Clinical Significance and Potential Role of C-Reactive Protein in Chronic Inflammatory and Neurodegenerative Diseases. Front Immunol. 2018; 9:1302-.
  5. Sproston NR, et al. Role of C-Reactive Protein at Sites of Inflammation and Infection. Front Immunol. 2018; 9:754-.
  6. Pepys MB, et al. C-reactive protein: a critical update. J Clin Invest. 2003; 111(12):1805-12.
  7. Bautista LE, et al. Independent association between inflammatory markers (C-reactive protein, interleukin-6, and TNF-alpha) and essential hypertension. J Hum Hypertens. 2005; 19(2):149-54.
  8. The Interleukin-6 Receptor Mendelian Randomisation Analysis (IL6R MR) Consortium. The interleukin-6 receptor as a target for prevention of coronary heart disease: a mendelian randomisation analysis. The Lancet. 2012; 379(9822):1214-24.
  9. Diez-Pina JM, et al. Tumor necrosis factor alpha as a marker of systemic and local inflammation in "healthy" smokers. Int J Gen Med. 2009; 2:9-14.
  10. Monastero RN, et al. Cytokines as Biomarkers and Their Respective Clinical Cutoff Levels. Int J Inflam. 2017; 2017:4309485-.
  11. NHS. Coeliac disease. Date Accessed: 23/11/20. [Available from: https://www.nhs.uk/conditions/coeliac-disease/causes/].
  12. Vadell AKE, et al. Anti-inflammatory Diet In Rheumatoid Arthritis (ADIRA)—a randomized, controlled crossover trial indicating effects on disease activity. The American journal of clinical nutrition. 2020; 111(6):1203-13.
  13. Marcason W. What Is the Anti-Inflammatory Diet? Journal of the American Dietetic Association. 2010; 110(11):1780.
  14. WorldCat. Anti inflammatory diet. Date Accessed: 23/11/20. [Available from: https://www.worldcat.org/search?qt=worldcat_org_bks&q=anti+inflammatory+diet&fq=dt%3Abks].
  15. Ricker MA, et al. Anti-Inflammatory Diet in Clinical Practice: A Review. Nutrition in clinical practice : official publication of the American Society for Parenteral and Enteral Nutrition. 2017; 32(3):318-25.
  16. Li J, et al. Dietary Inflammatory Potential and Risk of Cardiovascular Disease Among Men and Women in the U.S. Journal of the American College of Cardiology. 2020; 76(19):2181-93.
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  19. Zwickey H, et al. Effect of the Anti-Inflammatory Diet in People with Diabetes and Pre-Diabetes: A Randomized Controlled Feeding Study. J Restor Med. 2019; 8(1):e20190107.
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  21. Shivappa N, et al. Designing and developing a literature-derived, population-based dietary inflammatory index. Public Health Nutr. 2014; 17(8):1689-96.
  22. Neale EP, et al. Consumption of a healthy dietary pattern results in significant reductions in C-reactive protein levels in adults: a meta-analysis. Nutr Res. 2016; 36(5):391-401.
  23. Schwingshackl L, et al. Mediterranean dietary pattern, inflammation and endothelial function: A systematic review and meta-analysis of intervention trials. Nutrition, Metabolism and Cardiovascular Diseases. 2014; 24(9):929-39.
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  29. Ristow M, et al. Antioxidants prevent health-promoting effects of physical exercise in humans. Proc Natl Acad Sci U S A. 2009; 106(21):8665-70.
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