Inflammation and diet

Chronic low-level inflammation is a feature of most chronic health conditions. The link between inflammation and diet is multi-factored and can’t be reduced to individual foods or nutrients.

What is inflammation?

Inflammation is an important mechanism of the immune response. Under normal circumstances, it acts as a local response to cellular injury.

The characteristics of inflammation are increased blood flow, capillary dilatation, leukocyte infiltration, and localised production of chemicals (1).

The signs and symptoms of inflammation include heat, redness, swelling, pain, and loss of function (2).

Types of inflammation

Broadly speaking, there are two types of inflammation: acute and chronic.

• Acute: This is the “good” kind of inflammation, which happens in response to an acute stressor such as infection or injury (2).
• Chronic: This is the “bad” kind of inflammation, a.k.a. “low-grade” or “systemic” inflammation. It is the common feature of chronic conditions including metabolic syndrome, non-alcoholic fatty liver disease, type 2 diabetes, cardiovascular disease, Alzheimer’s disease, certain cancers (colon, pancreatic, breast), and autoimmune diseases (1, 2, 3). These conditions are are highly prevalent in Westernised societies and are on the rise in developing countries.

Factors that affect inflammation

Adipose tissue

Overweight and obesity happens when there are too many adipose (i.e. fat) cells and/or when those cells get too big (i.e. adipose tissue hypertrophy). The latter is associated with infiltration of certain immune cells and the secretion of pro-inflammatory mediators (1).

Gut health

Gut permeability allows the entry of bacterial lipopolysaccharides (LPS) from our digestive system into the the bloodstream (1). LPS is a component of the membrane of generally pathogenic bacteria which stimulates chronic inflammation.

It is also known that the gut microbiome can influence the risk of autoimmune conditions such as type 1 diabetes, coeliac disease inflammatory bowel disease and rheumatoid arthritis (1).

Short-chain fatty acids such as acetate, propionate and butyrate, which are produced by bacterial fermentation of certain dietary fibres, positively affect inflammatory processes (1). These metabolites are also crucial for maintaining gut integrity, preventing gut permeability.

Dietary fats

Fats taken in the diet can impact inflammation in a number of ways:

• Because fats are energy-dense, they can lead to an increase on body mass and adipose tissue (1), which can lead to inflammation as seen above
• Dietary fats get incorporated into cell membranes (1)
• They can modulate or serve as precursors for inflammatory mediators (1)
• They can promote the translocation of microbial products into bloodstream, triggering inflammation (2)

Anti-inflammatory fats

Long-chain omega-3 polyunsaturated fatty acids such as eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) have been shown to have anti-inflammatory effects (1, 3).

Pro-inflammatory fats

Trans fatty acids, mainly present in processed and fast foods, are generally known to induce inflammation (3).

Saturated fatty acids, mainly present in animal fats and coconut oil, have been shown to be inflammatory in many rodent studies, however there is limited evidence in humans. It seems that the effects may depend on genetic variation and/or gut microbiome status or composition (2).

Carbohydrates

The increase of blood glucose after meals can cause oxidative stress and inflammation. The magnitude and duration of this post-prandial glucose rise has a direct impact on the inflammatory process.

With regard to the type of carbohydrate, high glycaemic index (GI) carbohydrates tend to activate pro-inflammatory pathways.

In contrast, low GI carbohydrates may protect against systemic inflammation.

Flavonoids

Flavonoids, a type of phytochemicals present in many foods, can have a potent anti-inflammatory effect. The effects are likely due to the modulation of intracellular signalling cascades, an effect on gene expression and interaction with the mitochondria (the energy-producing organelles in our cells) (1).

Pre-natal status

The nutritional status of the mother affects the baby in many ways. When it comes to inflammation, it has been observed that babies born to obese mothers are exposed to increase cytokine levels in the placenta. The iron status of the mother during pregnancy can also affect the inflammatory status of her offspring (1).

Dietary patterns and inflammation

Of course, we don’t eat nutrients but foods that normally fall under a dietary pattern.

The Western-style, a.k.a. standard American/Australian diet (S.A.D.) is commonly recognised as a pro-inflammatory dietary pattern (3). It is characterised by:

• Processed foods
• Refined sugar
• Trans and saturated fats
• Energy density
• Lack of dietary fibre, vitamins and minerals

On the other hand, Mediterranean-style diets have been shown to be highly anti-inflammatory (3, 4). More recently, the Nordic diet has also been shown to have similar benefits, however currently available studies are limited in number and geographical reach (4). Both diets are based on:

• Vegetables
• Fruits
• Whole grains
• Legumes
• Nuts
• Fish

The main differences between both diets are the use of local produce and the type of oil used in cooking (olive oil in the Mediterranean diet vs canola oil in the Nordic diet) (4).

Summary and recommendations

• Acute inflammation is good and should not be dampened
• Chronic low-grade inflammation should be minimised
• Certain nutrients have been linked with increased/decreased inflammation
• The effect is likely due to a combination of factors
• It is more useful to look at dietary patterns than individual nutrients
• Western-style diets associated with increased inflammation

References

1. Minihane AM, Vinoy S, Russell WR, Baka A, Roche HM, Tuohy KM, et al. Low-grade inflammation, diet composition and health: current research evidence and its translation. Br J Nutr. 2015 Oct;114(7):999–1012.
2. Fritsche KL. The science of fatty acids and inflammation. Adv Nutr. 2015 May;6(3):293S-301S.
3. Christ A, Lauterbach M, Latz E. Western Diet and the Immune System: An Inflammatory Connection. Immunity. 2019 Nov;51(5):794–811.
4. Lankinen M, Uusitupa M, Schwab U. Nordic Diet and Inflammation-A Review of Observational and Intervention Studies. Nutrients. 2019 Jun;11(6).

[Photo by Guido Jansen on Unsplash]

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