Role of Dietary Lipids on Immune Modulation
By Prithu Nath
A suppression of immune system functions implies an inability of the immune response to eliminate efficiently the infectious agents.
Dietary Lipids or the fats we eat are known to influence the Functioning of the Immune System, therefore during the Covid Pandemic, balancing of the Dietary Fats is a very important aspect.
Certain Dietary Lipids may suppress the Immune System whereas certain others may over activate the Immune system, hence a balance must be maintained.
Fatty acids are the key structural components of phospholipids and triglycerides, and thereby affect nearly every facet of eukaryotic physiology. In addition to forming the building blocks of membranes and functioning as a currency of energy storage, fatty acid molecules promote health in a diverse number of ways. For example, fatty acids act as soluble signals for intracellular communication, affect membrane fluidity, and have been directly linked to lifespan regulation [1–3]. Conversely, excess stores of fatty acids in triglycerides lead to atherosclerosis and type 2 diabetes . Thus, it is important to understand how individual fatty acids affect key physiological processes within a cell.
Fish Oil is known to delay the clearance of Influenza Viruses whereas the CLA from Ghee is considered as an important biologically-active compound of food due to its proven anti-carcinogenic, anti-allergic and anti-inflammatory properties [8, 9].
Medicinal value of Cow Ghee aids in fast absorption and digestion of food. Ghee stimulates the secretion of stomach acids to aid in digestion, while other fats and oils, can slow down the body’s digestive process and sit heavy in the stomach.
High CLA fed diet lowers the lipid peroxidation process and inturn protects the cells from its harmful effects. Recent study by Varady et al.  has proved that oxidized fat increases the nuclear concentration of NF-κB and Nrf2 and transcript levels of oxidative stress-responsive genes coding for aldo–keto reductase 1B8, vanin-1, glutathione peroxidase 1, and superoxide dismutase-1. Hence, CLA plays a definite role in taking care of oxidative stress in rats and removing the free radicals from the biological system.
The study shows that high CLA enriched ghee increases the antioxidant enzyme activities such as CAT, SOD and GST activities; which concludes its antioxidant nature. Feeding of high CLA enriched ghee also lead to a decrease in cholesterol, triglyceride and high density lipoproteins and inturn, decreased the low density lipoproteins, which finally lead to the reduction in atherogenic index, which proves its antiatherogenic property. The present study indicates that high CLA enriched ghee (clarified butter) has antioxidant and antiatherogenic activities suggesting that ghee can be as an important food component for decreasing the risk of cardiovascular diseases.
The importance of cholesterol for brain function is attested by the fact that brain itself has >2% cholesterol by weight. However, the mechanism by which cholesterol affects memory is unknown . Cholesterol is crucial for synapse generation and formation of synaptic vesicles . Additionally, cholesterol is considered to be essential for remodeling neuronal membranes and growing new terminals, either during synaptic plasticity or in response to a neurodegenerative insult . Manipulations of cholesterol in animals have shown a number of different relationships between cholesterol and memory.
Ghee, also known as clarified butter or anhydrous milk fat, is prepared by heating butter or cream to just over 100°C to remove water content by boiling and evaporation, then filtering out the precipitated milk solids. Ghee is known as ghrta (commonly spelled ghrita) in Sanskrit. Ayurveda has traditionally considered ghee to be the healthiest source of edible fat, with many beneficial properties. According to Ayurveda, ghee promotes longevity and protects the body from various diseases. It increases the digestive fire (agni) and improves absorption and assimilation. It nourishes ojas, the subtle essence of all the body’s tissues (dhatus). It improves memory and strengthens the brain and nervous system. It lubricates the connective tissues, thereby rendering the body more flexible. With regard to the three doshas (organizing principles that govern the physiology), ghee pacifies Vata and Pitta and is acceptable for Kapha in moderation.
Ghee is heavily utilized in Ayurveda for numerous medical applications, including the treatment of allergy, skin, and respiratory diseases. Many Ayurvedic preparations are made by cooking herbs into ghee. Ghee carries the therapeutic properties of herbs to all the body’s tissues. It is an excellent anupana (vehicle) for transporting herbs to the deeper tissue layers of the body. Proper digestion, absorption, and delivery to a target organ system are crucial in obtaining the maximum benefit from any therapeutic formulation; the lipophilic action of ghee facilitates transportation to a target organ and final delivery inside the cell since the cell membrane also contains lipid. A study that compared different forms of herbs and herb extracts found that the efficacy increased when they were used with ghee, compared to usage in powder or tablet form.
Ghee is considered sacred and used in religious rituals as well as in the diet in India. In ancient India, ghee was the preferred cooking oil. It was considered pure and was felt to confer purity to foods cooked with it. Ghee and other similar products such as samn (variant of the Arabic term samn) are used in many parts of the world.
Studies are available where cow ghee was used as vehicle/medium with other herbal drugs having Health and Memory enhancing actions. In study conducted on Kushmandadi Ghrita  and Panchagavyaghrita  where cow ghee was used as vehicle, no nootropic activity was observed with cow ghee group alone, using EPM and MWM animal experimental models. Many Ayurvedic preparations having action on CNS are in Ghrutaform. In such preparation Cow Ghee is used as vehicle due to its lipoidal nature and it can easily cross blood brain barrier (BBB) .
Fat is an essential nutrient that the body needs to function fully. Fats in the diet help the body absorb vitamins and minerals and serve other vital roles. Fat stored in body tissues is critical for:
- energy storage and metabolism
- body temperature regulation
- insulation of the vital organs
FISH OILS LEAD TO AN IMPAIRMENT OF THE IMMUNE RESPONSE TO CLEARANCE OF INFLUENZA GROUP OF VIRUSES:
A possible explanation for the effects of lipids upon immune system modulation may be attributed to changes in cytokine production after dietary lipid administration. Thus, as mentioned previously, production of IL-1, TNF, IL-2, IL-6 and IFN-γ have been modified by dietary lipids, and particularly by fish oil. A recent finding has underlined the important role of dietary lipids on the IFN-γ production during experimental infection with L. monocytogenes. IFN-γ production from serum or spleen cells fed a fish oil diet was markedly increased during the infectious process with L. monocytogenes. However, these authors suggest that the increase in the production of IFN-γ may be due to an alteration in the expression of IFN-γ receptor function rather than changes in the production of this cytokine . On the contrary, a recent study has reported that fish oil diet supplied to mice promotes a significant reduction of IFN-γ production as well as an impairment of influenza virus clearance from lung after experimental infection, whereas virus clearance was more efficient in groups fed a diet containing SFAs . In addition, the infection of mice with influenza virus impaired T lymphocyte cytotoxicity and had no effect on NK cell activity, despite an increase in lymphocyte proliferation exerted by the diet containing fish oil , therefore, this fact could be responsible for the delayed virus clearance . Numerous studies have carried out the isolation of inoculated bacteria from spleen or liver after experimental infection and the results confirm that diets containing fish oil increase the recovery of microorganisms from these organs. In fact, Shinomiya  observed an increase in the number of L. monocytogenes isolated from the liver of mice fed a high-fat diet. Similarly, Fritsche  demonstrated that the clearance of L. monocytogenes from spleen or liver was greatest in the group fed fish oil , whereas clearance from mice fed a diet containing hydrogenated coconut oil as well as survival percentage were lower . Bacterial enumeration of M. tuberculosis from spleens was also increased in animals fed n-3 PUFAs . However, as mentioned previously, several lines of evidence have indicated that recovery of L. monocytogenes from spleens of experimentally infected animals fed a diet rich in SFAs (lard or hydrogenated coconut oil diet) was significantly diminished [23,29]. Reduction of eicosanoid products, as a consequence of PUFAs administration could explain in part the defect in bacterial clearance that implies reduced phagocytic activity and killing of bacteria . Nevertheless, it is noteworthy that many discrepancies have been reported concerning the beneficial or detrimental effects of dietary lipids upon natural resistance as a consequence of immune system modulation. Thus, animals fed diets containing melted beef tallow or fish oil and infected with four different classes of microorganisms or pathogenic agents (L. monocytogenes, Pseudomonas aeruginosa, Candida albicans and murine cytomegalovirus) did not modify the susceptibility to any of these systemic infections. Therefore, these authors concluded that the anti-inflammatory effects of fish oil are not related to an increased risk to infectious pathogens . In contrast, the reduction of bacterial clearance has not only been observed in mice, but also in neonatal rabbits fed a diet containing fish oil. Bacterial clearance of Staphylococcus aureus was lower in these animals than those fed a diet containing safflower oil . Nevertheless, the bactericidal activity of macrophages from rats fed diets containing EPA or DHA did not impair the bactericidal function of these cells incubated with S. aureus.
The effect of dietary lipid manipulation on immune response has also been analyzed in animals infected with viruses. In this way, findings from a recent study carried out with influenza virus are in accordance to previous results from animals infected with bacteria. Although the virus strain used in this study did not cause death, a delay in virus clearance has been reported in mice fed fish oil. These effects may be attributed to a reduced IFN-γ production, as well as a reduction of antibody synthesis as a consequence of dietary lipid administration . On the contrary, mice infected with a murine AIDS (LP-BM5, a murine retrovirus) and fed with a diet containing fish oil have demonstrated a reduction in the progression of murine AIDS by modulating macrophage-derived cytokines as well as IL-2 . This diet also prevented the depression of ConA-stimulated splenocyte proliferation after infection with this virus [41,42].
5 Concluding remarks
The important role of dietary lipids in the modulation of the immune system may be applied in the treatment of autoimmune abnormalities, such as rheumatoid arthritis, psoriasis, multiple sclerosis, etc, because, n-3 PUFAs may diminish the incidence and severity of immunologically mediated diseases as a consequence of a alteration of different immune parameters (Fig. 1). However, this event has a detrimental effect on the host resistance to infectious microorganisms or pathogenic agents, such as bacteria, parasites or viruses. Although this argument generates several contradictory results, due particularly to numerous studies that have described an increase of natural resistance to experimental infection after dietary lipid administration (Table 1).
CLA FROM GHEE & IT’S BENEFICIAL EFFECTS
Conjugated linoleic acid (CLA) is an important food component that consists of a mixture of positional and geometric isomers of linoleic acid (cis − 9, cis − 12, C18:2) with two conjugated double bonds at various carbon positions in the fatty acid chain . CLA is formed as an intermediate during the biohydrogenation of linoleic acid by linoleic acid isomerase from the rumen bacteria Butyrivibrio fibrisolvens or from the endogenous conversion of t-11, C18:1 (vaccenic Acid), another intermediate of linoleic or linolenic acid biohydrogenation, by Δ9-desaturase in the tissues . Milk fat is the richest natural dietary source of CLA which contains an average 4.5 mg CLA/g of fat . CLA is considered as an important biologically-active compound of food due to its proven anticarcinogenic, antiallergic and anti-inflammatory properties [8, 9]. The CLA isomer (18:2 c-9, t-11), also known as rumenic acid, has been recognized by its anti-inflammatory action in healthy people35.
TYPES OF DIETARY FATS
Nutrition experts classify fats into three main groups: Saturated, unsaturated, and trans fats.
These fats have single bonds between their molecules and are “saturated” with hydrogen molecules. They tend to be solid at room temperature.
Food sources that contain high levels of saturated fat include meat and dairy products, such as:
- high-fat cuts of meat
- coconut oil
- palm oil
A 2015 meta-analysis found that medium-chain triglycerides (MCTs) might be the most healthful type of saturated fat. Coconut, for example, provides plenty of MCTs.
Unsaturated fats contain one or more double or triple bonds between the molecules. These fats are liquid at room temperature in oil form. They also occur in solid foods.
This group breaks down further into two categories, called monounsaturated fats and polyunsaturated fats.
Dietary sources of unsaturated fats include:
- avocados and avocado oil
- olives and olive oil
- peanut butter and peanut oil
- vegetable oils, such as sunflower, corn, or canola
- fatty fish, such as salmon and mackerel
- nuts and seeds, such as almonds, peanuts, cashews, and sesame seeds
Mediterranean diets are typically high fat but have links to good heart health. Learn more about this diet here.
These fats take a liquid form that converts to solid fats during food processing techniques.
Some meats and dairy products contain small amounts of trans fats, but they play a role in processed foods.
However, since 2015, the Food and Drug Administration (FDA) has taken steps to eliminate partially hydrogenated oils (PHOs), a significant source of trans fats, from processed food. Manufacturers had until the beginning of 2020 to stop adding PHOs to their food products.
Examples of food products that may still contain trans fats include cookies, crackers, doughnuts, and fried foods. However, trans fats are becoming less and less present.