FADS1 Gene Detail
FADS1 is a member of the fatty acid desaturase (FADS) gene family and is one of 3 fatty acid desaturates in this region, the others being FADS2 and FADS3. Desaturase enzymes regulate the unsaturation of fatty acids by introducing double bonds between defined carbons of the fatty acid chain. FADS1 and FADS2 code for the enzymes delta 5 and delta 6 desaturate activities, respectively. Less is known about FADS3.
Variations in the FADS1 and FADS2 gene cluster have been found to affect polyunsaturated fatty acid (PUFA) metabolism and have been associated with changes in blood concentrations of long chain PUFAs and cholesterol. PUFAS play a role in many physiological processes including regulating immunity and inflammation, impacting brain and eye development and function, energy production and maintaining cell membrane integrity. Alterations in PUFA metabolism and blood concentration therefore impact on these functions.
Over last 75 years we have seen a drastic change in the human diet. The modern Westernized diet has seen changes in the quantity and quality of our food (the types of food we are eating) and these have been largely driven by technological changes in food production and processing, with the addition of sugars, refined grains and oils to provide high calorie, tasty foods.
There is increasing evidence that many of these changes have resulted in an increase in obesity and interactions that are responsible for a rise in localised and systemic inflammation which then contributes to a wide range of conditions such as cardiovascular disease, diabetes, cancer, asthma, allergies, joint diseases, skin and digestive disorders, dementia, Alzheimer’s disease.
The PUFA pathway is made up of two parallel and competing pathways, the omega 6 (n-6) pathway and the omega 3 (n-3) pathway. Linoleic acid (C18:2n-6; LA), at the start of omega 6 pathway, and alpha linolenic acid (C18:3, n-2; ALA), at the start of the Omega 3 pathway, are converted into long chain polyunsaturated fatty acids (LC-PUFAs) by alternate desaturation and elongation steps. Two fatty acid desaturase enzymes (delta 6 desaturase, encoded for by FADS2 and delta 5 desaturase, encoded for by FADS1) and an elongase enzyme, increasing carbon-carbon double bonds and increasing chain length, are involved in this conversion process into LC-PUFAs that can be used by the cell membrane.
Both LA and ALA are considered to be essential fatty acids because they cannot be synthesized by humans and need to be obtained from the diet. LA is the most abundant PUFA in modern diets, contributing more than 85-90% of ingested PUFAs and approximately 6-7% of total calories consumed. It is found in vegetable oil products (such as soybean, corn, palm oils as well as margarine and shortenings). Dietary intake of LA has increased 2-3 fold over the last 50 years in the modern Westernized diet, largely from an increased intake of cooking oils and processed foods. It is thought that the American Heart Association (AHA) Central Committee Advisory Statement from 1961 calling for the replacement of saturated fats with unsaturated fats in processed foods and the updated guidelines from AHA in 2009 recommending that human diets include 5-10% total energy intake of n-6 into their diets, lead to this increase. ALA is found in chia seeds, flaxseeds and flaxseed oil, walnuts, soybean, tofu and edamame beans and seaweed, nori and spirulina It makes up approximately 0.5-1.5% of our dietary intake. Due to the significant increase in dietary LA and reduced intake of total n-3 LCPUFAs levels (by approximately 40%) there has been a large shift in the ratio of dietary n-6/n-3 C18 PUFAs consumed from 5:1to >10:1.
Figure 1: LC PUFA Biosynthetic Pathway.
Chilton FH, Murphy RC, Wilson BA, Sergeant S, Ainsworth H, Seeds MC, Mathias RA. Review. Diet-Gene Interactions and PUFA Metabolism: A Potential Contributor to Health Disparities and Human Diseases. Nutrients 2014, 6, 1993-2022.
The omega 3 (ALA) and omega 6 (LA) compete early on in the pathway. The desaturation steps have been recognized as the rate limiting steps and FADS1 and FADS2 are two important genes that play a critical role here. In the initial desaturation step, n-6 LA is converted into gamma linolenic acid (GLA, 18:3, n-6) and n-3 ALA to stearidonic acid (SDA, 18:4, n-3) by the enzyme encoded for by the gene fatty acid desaturase 2 (FADS2).
GLA is then elongated to dihomo-y-linolenic acid (DGLA, 20:3, n-6) and SDA to eicosatrenoic acid (ETA, 20:4, n-3) by an elongase step. The second desaturation step converts DGLA (2-:3, n-6) to arachidonic acid (AA, 20:4, n-6) and eicosatetraenoic (ETA, 20:4, n-3) to eicosapentaenoic acid (EPA 20:5, n-3) by the enzyme encoded by the gene fatty acid desaturase 1 (FADS1). EPA is eventually converted to docosahexaenoic acid (DHA) using two elongation. Graphical representations of the PUFA pathway, taken from Chilton et al. (2014) and Mathias et al. (2014) are included below.
Arachidonic acid (AA) can then be metabolised via cyclooxygenase and lipoxygenase pathways into eicosanoids such as prostaglandins, thromboxanes and leukotrienes. Arachidonic acid (AA) and its metabolites, once produced, play important roles in immunity and inflammation through their ability to impact on normal and pathophysiological processes. Eicosanoids have been shown to increase acute and chronic inflammation in a number of human diseases including cardiovascular disease (stroke, heart disease and atherosclerosis), arthritis and asthma. Eicosanoids impact on bronchoconstriction, vascular permeability, platelet aggregation and leukocyte recruitment, all contributing to diseases.
DHA is the most abundant fatty acid in the brain and retina. It has been shown to have strong anti-inflammatory properties and plays a critical role in neurogenesis and neural plasticity. Adequate dietary DHA levels are essential for visual, neural and cognitive development in the developing foetus and young infants.
Figure 2: Biosynthetic pathway of Omega 3 and Omega 6.
Mathias RA, Pani V, Chilton FH. Curr Nutr Rep. 2014, June; 3(2): 139-148.
PUFA’s, Our Diet And Our Health
The typical Westernized diet is rich in Omega 6 PUFAs and poor in Omega 3 PUFAs, especially EPA and DHA.
Our main dietary source of AA can be readily obtained from the human diet and is found in organ meats, eggs, poultry and meats of grain fed animals and daily intake is said to vary from 50mg to greater than 500mg. Our main dietary source of EPA and DHA is seafood, particularly oily fish. Consumption of fatty fish, omega 3 fortified foods or dietary supplements such as fish oil, algal oil or krill oil can increase Omega 3 content of the diet. Consumption of fish oils have been found to reduce cardiometabolic markers including blood triglycerides (TAG) and inflammatory mediators, which may reduce risk for cardiovascular and metabolic diseases. Consuming a meal of oily fish, such as albacore tuna, mackerel or salmon can provide 500mg – 2g of Omega 3s LC PUFAs, however in the modern-day Westernised diet, average intake of n-3 LCPUFAs is ≤100mg per day. EPA and DHA fish oil supplements increase tissue and circulating levels of n-3 LCPUFAS.
Since LA and ALA share the same enzymes in the early steps of the pathway, the increase of LA and resulting n-6 metabolic intermediates, as a consequence of modern Westernized diet, might cause reductions in the synthesis of n-3 LCPUFAs, resulting in an even higher ratio of n-6: n-3 LCPUFA ratio. It is thought that the competition between LA and ALA and their intermediates down the PUFA biosynthetic pathway, rather than a reduced dietary consumption of ALA, causes the reduction in n-3 LCPUFAs. A reduced intake of n-3 LCPUFAs is also likely to have affected this. Hibbeln and colleagues suggested that the ingestion of human n-3 PUFAs could be reduced 10 fold if dietary intake of n-6 PUFAs, particularly LA, was lowered to less than 2% of total energy intake (2). It has also been suggested that when concentrations of LA are very high, the PUFA biosynthesis pathway from LA to AA is saturated, which limits the amount of AA that can be made.
SNPs in the FADS gene influence the degree of endogenous conversion of ALA into EPA and DHA. Individuals carrying the variant allele in one or more SNPs in FADS1 and/or FADS2 have been reported to have a reduction in desaturase activity, resulting in lower levels of EPA.
Shaeffar and colleagues, cited by Chilton, found that in a European population, the variant alleles of the SNPs in a region encompassing FADS1 and the promoter of FADS2 were strongly associated with increased levels of LA, eHibbeln and colleagues suggested that the ingestion of human n-3 PUFAs could be reduced 10 fold if dietary intake of n-6 PUFAs, particularly LA, was lowered to less than 2% of total energy intake. It has also been suggested that when concentrations of LA are very high, the PUFA biosynthesis pathway from LA to AA is saturated, which limits the amount of AA that can be madeicosadienoic acid, DGLA and ALA and decreased levels of GLA, AA, adrenic acid and DPA.
Variations in FADS1 and 2 gene cluster can impact on cardiac health, with SNPs in FADS1 and 2 having been associated with changes in lipid metabolism and cardiovascular disease. Genome Wide Association Studies (GWAS) have identified several loci in the FADS gene cluster at which variant alleles have been associated with lower total cholesterol (TC), low density lipoprotein (LDL) cholesterol, high density lipoprotein (HDL) cholesterol levels and triglyceride (TG) concentrations, suggesting that alterations in desaturase activity may impact on plasma lipoprotein levels. Variations in the FADS1 and FADS2 genes have also been associated with glucose metabolism and type 2 diabetes, as well as changes in circulating CRP levels, a marker of whole-body inflammation, certain disease conditions such as metabolic syndrome and myocardial infarction.
SNP Description and Amino Acid Change
As already mentioned, variations in FADS genes impact on PUFA metabolism and blood concentrations. One of the most common SNPs that has been researched and found to impact the PUFA metabolism, is rs174537, a SNP near the FADS1 gene on chromosome 11. The SNP sees a replacement of G>T. Wild type is GG, heterozygote type is GT and homozygous type TT. G is the risk allele. Studies also refer to the minor allele (TT or TG) and the major allele (GG).
Individuals carrying the GG genotype are thought to be efficient converters with regard to delta5 desaturase (FADS1) enzymatic efficiency resulting in an increased conversion of DGLA to AA and increased AA levels in the blood and subsequent increased inflammation, whereas GT and TT are modest converters and non-converters respectively.
This SNP has been found to account for 18.6% of the additive variance in AA concentrations.
The dietary and lifestyle trigger that appears to activate this gene is an increased intake of dietary LA and reduced intake of EPA and DHA. Phenotypic traits that have been seen, in the presence of a high intake of LA, are increased cholesterol levels, increased inflammation, increased presence of inflammatory conditions and diabetes.
Studies Linked To The Effects Of FADS rs1745237
Tanaka et al. conducted a study on 1075 participants from the inChianti study on ageing to identify genetic contributors of plasma PUFA concentrations and found that the region encoding the three fatty acid desaturases (FADS1, FADS2, FADS3) showed the strongest evidence for association, with SNP rs174537 near FADS1 showing the most significant association for arachidonic acid (AA). The minor allele homozygotes (TT) for this SNP had lower AA levels compared to the major allele homozygote (GG) and SNP rs174537 accounted for 18.6% of the additive variance in AA concentrations. This SNP was also associated with levels of eicosadenoic acid (EDA) and eicosapentaenoic acid (EPA). Participants carrying the allele, that was associated with higher levels of AA, EDA and EPA also had higher LDL and total cholesterol levels and participants carrying the T allele, associated with lower AA levels, had decreased total cholesterol and LDL levels. The effect of this rs174537 SNP were confirmed in an independent sample of 1076 participants in the GOLD study.
Li et al, based on their previous research, found that the rs174537 T allele is associated with a lower risk of coronary artery disease, compared to carriers of the rs174537 G allele. They went on to explore whether plasma fatty acids and SNPs in the fatty acid desaturase (FADS) gene associated with Type 2 diabetes mellitus (Type 2 DM) and coronary artery disease (CAD). They hypothesized that SNPS in the FADS gene will influence the desaturase activity, thereby altering the characteristics of plasma free fatty acids and risk of Type 2 DM and CAD. 827 individuals were recruited at Zhongnan Hospital of Wuhan University and of these 234 patients had Type 2 DM, 200 patients had CAD, 185 patients had Type 2 DM and CAD and there were 253 healthy controls.
They found that Type 2 diabetes patients with rs175437 GG genotype had elevated plasma levels of total cholesterol, low density lipoprotein (LDL) cholesterol, FPG, GLA, DGLA and arachidonic acid (AA) and delta 6 desaturase levels and that they were at increased risk of developing type 2 diabetes and CAD, due to the influence on desaturate activity (Li). The minor T allele of rs175437 was significantly associated with n-3 fatty acid concentrations in the three groups. The findings also suggested to a certain extent that elevated levels of EPA and DHA might protect Type 2 diabetics against CAD.
In a Korean cohort, the minor T allele at SNP rs174537, was associated with lower levels of AA, higher levels of LA and a lower number of CAD patients compared to controls. In the same study, the proportion of AA in serum phospholipids has a positive association with LDL cholesterol, ox-LDL and malondialdehyde in controls. Three years after the initial examination, there was an association between the GG genotype for rs175437 and increased cardiovascular risk factors (intermediate phenotypes) i.e. AA levels, LDL cholesterol, ox-LDL, IL6 and urinary 8-epi-prostaglandin F (2α) comparted to the TT genotype. The data suggested that GG genotypes have higher levels of intermediatory phenotypes (such as these cardiovascular risk factors mentioned) at a selected point in time and that age associated changes are greater in GG genotypes.
Hong et al. conducted a study to investigate associations between SNPs in the FADS cluster and age-related changes in PUFAs serum phospholipids and oxidative stress markers. 122 middle aged non-obese men without any known diseases at baseline were followed for three years. Four SNPS were looked at, one of these being rs174537. At baseline, men carrying the rs174537 T allele had lower arachidonic acid and AA/linolenic acid and higher interleukin levels (Il-6) levels than rs1745377 GG counterparts. After three years, these GG men had significantly increased AA, AA/DGLA, docosapentaenoic acid (DPA), low density lipoprotein cholesterol, and oxidised LDL cholesterol but decreased eicosatrienoic acid, EPA/ALA and IL-6. After three years, the rs174537 T group had lower AA, AA/DGLA, EPA, DLA, EPA/ALA than the GG group. The major findings of the study were that polymorphisms in FADS may affect age associated changes in serum phospholipid LC PUFAS, delta 5 desaturase activity and oxidative stress in middle-aged non-obese men and the rs174537 T allele did not show age associated increases in AA and delta 5 desaturase activity that was seen with the rs174537 GG group. It should be noted that the study has a small sample size (n=160), PUFAs were expressed as a % of total FAs in serum phospholipids and the actual dietary intake of PUFAs was not looked at, but dietary intake of total fat % was looked at and did not change during the follow up period. It is also important to note that these results were relevant to South Korean, non obese, middle aged men and data cannot be generalised to other populations.
As mentioned above, genetic variants associated with higher levels of AA have also been associated with raised levels of markers of systemic inflammation and incidence of certain inflammatory disorders. The results of a study by Sergeant et al. showed that African Americans with diabetes/metabolic syndrome tend to have a marked increase in AA and in the frequency of alleles that favour AA synthesis compared to European American populations in the US. European Americans and African Americans took part in this study. African Americans were found to have higher levels of circulating AA than European Americans, however levels of fatty acid precursors, LA and GLA, were not different. This study found that 81% of African Americans and 46% of European Americans in the DHS population had the homozygous GG allele which is associated with increased AA levels for SNP rs174537. In this study population, no African American had the homozygous TT allele, however 18 out of 159 European Americans carried the homozygous TT allele for rs174537. Significant differences were seen in AA and DGLA and AA:DGLA ratios, an estimate of FADS1 activity, between GG, GT and TT in the European populations. These differences were not seen in the African American population, however in a follow up study with a bigger sample size, highly significant genotypic differences in circulating levels of AA, DGLA and AA:DGLA ratios were found in a subset of African American study population, comparable to that in DHS European Americans. Large differences in allele frequencies at rs174537 in different HapMAp populations have been seen.
Populations from Africa have much higher frequencies of GG alleles and low frequencies of TT alleles whereas endogenous populations from America show low frequencies of GG alleles and higher frequencies of TT alleles and some other populations looked at lie in the middle. With different populations having different frequencies of alleles, this paper suggests that the efficiency of LA to AA conversion is likely to be population specific.
Individuals carrying GG genotype for rs174537 are thought to be efficient converters with regard to delta5 desaturase (FADS1) enzymatic efficiency, and GG and GT modest converters and non-converters respectively. AA is considered to play a central role in inflammation and increasing dietary LA levels is likely to impact certain populations e.g. African Americans, having a higher proportion of ‘efficient converters’ of LA to AA, possibly leading to higher levels of circulating AA. Conditions such as obesity, type 2 diabetes and hypertension have been seen to disproportionately affect African Americans, where-as only 1-2% of Africans on African continent have Type 2 diabetes, however there is an 11-13% incidence of people with African descent consuming a Westernised diet in industrialised nations. Many genetic markers and metabolic changes may be contributing to these differences, however these variations on the FADS gene cluster may increase risk as populations move towards more Westernized diets, especially since variants associated with elevated AA/LA ratio are related to higher systemic inflammation (measured by high sensitivity CRP) and increased risk of CAD. Studies support that AA plays a role in inflammation and at risk populations who have a higher proportion of ‘efficient converters’, may be affected more.
Dietary Omega 3 Intake, rs174537 And Health
Increased dietary intake of n-3 LC PUFAs has been found to increase D5D activity in the plasma in carriers of the minor (T) allele of SNP rs174537 on the FADS1 gene which may affect LC PUFA composition and result in health implications.
Al Hilal conducted a study to investigate the association of three FADS1-FADS2 SNPs and reconstructed haplotypes with proportions of LC PUFAs in plasma and erythrocytes, estimates of D5 and D6 activities and plasma lipid concentrations at baseline in a randomised control trial on healthy subjects. They then investigated the influence on genetic associations of supplements of EPA and DHA over 6 months. Supplements given were equivalent to 1-2 portions of fish per week. Their aim was to discover whether interactions between the SNP genotypes and n-3 LC PUFA dosage was a significant determinant of the proportions of plasma or erythrocyte LC PUFA, estimated desaturase activities or plasma lipids.
Data was analysed for 310 healthy males and females; approximately 20% who were non-white, with similar proportions of Asian and black participants. Three SNPs at the FADS1-FADS2 locus, rs174537, rs174561 and rs3834458, were genotyped. When looking at Omega 6, the minor alleles (T) of all SNPs were associated with a higher proportion of FADS1 product DGLA,20:3n-6 and lower proportions of FADS2 product alpha linolenic acid (GLA, 18;3 n-6), FADS1 product AA (20:4, n-6) and its derivative adrenic acid. On the Omega 3 side, minor alleles (T) were significantly associated with a higher proportion of FADS1 substrate alpha linolenic acid (ALA, 18-3 n-3) and lower proportions of FADS2 product eicosapentaenoic acid (EPA, 20:5 n-3) and derivatives docosapentanoic acid (DPA,22:5n-3) and docosahexaenoic acid (DHA, 22-6 n-3). Lower estimated activities of D5D and D6D were also seen in all carriers of the minor alleles of all three SNPS compared to homozygous carriers.
The second part of the study investigated the effects that supplementation with EPA and DHA for 6 months had on plasma and erythrocyte phenotypes. The effect of the treatment was meant to increase competition from the derivates of Omega 3 LC PUFAs supplements and decrease proportions of omega 6s. After supplementation, proportions of all n-6 PUFAs significantly decreased and those of n-3 LC PUFA significantly increased (with the exception of adrenic acid). Activity of D5D increased and D6D decreased. No significant changes in plasma lipid concentrations were seen.
When reviewing the effects of SNP associations with plasma and erythrocyte variables after dietary intervention, no significant differences in the proportions of LCPUFA between the common homozygotes and variant allele carriers were found for any of the three SNPs, nor were effects on plasma lipids seen, linked to genotype and dose, however significant effects of treatment on estimations of desaturase activity was seen, when stratified by genotype. Carriers of the minor T allele for rs174537 had significantly lower D5D activity than GG carriers in the placebo group, but when dosage was increased, this activity increased significantly in the T carriers but not in GG homozygotes in plasma. This remained significant after adjusting for age, BMI, ethnicity and gender and D5D activity at baseline. The significant increase in D5D activity post treatment showed a greater reduction in AA than in DGLA substrate. Changes in D5D and D6D activity as a result of EPA and DHA intake have been detected in previous controlled intervention studies and some studies, but not all, have established interactions between intake of n-3 PUFA or fatty fish and FADS genotypes.
0verall the study found a significant interaction between dietary n-3 LC PUFA intake and rs174537 genotype as a determinant of D5D activity in the plasma, with potential effects on LC PUFAs composition and health implications.
Omega 3 Supplementation And Cardiovascular Health
Evidence from studies supplementing with flaxseed oil or encapsulated EPA and DHA suggest that genetic variations in FADS 1 /2 can affect how a person responds to omega 3 fatty acid supplements.
A very small study by Roke and Mutch on 12 male adults aged 18-25 years, was done to assess the impact of a moderate daily dose of EPA and DHA fish oil supplements on cardiometabolic markers, fatty acid levels in serum and red blood cells (RBC) and whether these endpoints were influenced by SNPs in FADS1/2.
Fish oil supplements providing a total of 1.8g EPA/DHA (1200mg EPA and 600mg DHA) was given daily for 12 weeks, followed by an 8-week wash out period. The SNPs rs174537 in FADS1 was genotyped and rs174576 in FADS2 were genotyped. By week 12, participants had a reduction of 13% in triglyceride levels and 11% in their glucose levels, however these benefits were lost during the washout period, indicating the importance of continuous supplementation to maintain these benefits. No significant changes were seen in cholesterol parameters with fish oil supplementation. Within the first two weeks of supplementation, serum and RBC EPA levels increased by 25% and 18% respectively and serum and RBC DHA levels increased by 51% and 18% respectively. These increased levels all remained raised throughout the 12 week period, however during the washout period only EPA and DHA levels in RBC remained significantly elevated (by 37% and 24% respectively). Serum levels of AA decreased during supplementation, but significance is sporadic as there was great inter-individual variability. RBC AA levels reduced by 13% at week 12 (compared to baseline) and were still reduced (by 6% compared to baseline) by the end of the wash out period.
Genotyping results were presented for rs174537 only, as genotyping revealed identical allelic distribution for the two SNPs. Minor allele carriers (TT or TG) had significantly lower serum EPA levels at baseline.
The minor allele carriers for both SNPs experienced greater percentage change in RBC EPA levels during supplementation, compared to major allele carriers (GG), suggesting that genetic variation at this locus may affect an individual’s response to fish oil supplementation.
No significant difference in cardiometabolic markers (TAG or glucose levels, specifically) between the major (GG) allele and minor (GT and TT) allele was seen at any point in time in the study (tested at baseline, week 12 and week 20). Minor allele carriers (GT and TT) had 48% lower baseline serum EPA levels than major (GG) allele carriers. Minor allele carriers also saw a greater increase (based on % increase) in RBC EPA levels during supplementation compared to major allele carriers, however there was no difference in ALA levels in either serum or RBC between major and minor allele carriers, suggesting that changes in ALA were not responsible for this change in EPA levels. There were no significant differences in DHA (possibly due to less DHA vs. ALA in the supplement) or AA levels in serum or RBCs based on genotype.
Overall the study aligns with results from some other studies by Cormier et al, Gillingham et al and Al-Hilal et al. Given that minor allele carriers for SNPs in FADS1/2 gene cluster typically have lower baseline serum and plasma EPA and AA levels and that individuals with lower plasma AA levels appear to experience greater increases in these fatty acids with supplementation, it is thought that genotyping FADS1 and FADS2 genes and measuring baseline EPA levels may assist health care practitioners in personalising information on omega 3 supplement recommendations.
Limitations of this study should be noted, such as the inclusion of young males only since females typically have higher levels of DHA in their blood than males and experience changes in omega 3 levels during menstruation. The sample size was very small and individuals were generally healthy, however results were said to be in a high level of agreement with previous independent studies in large cohorts.
Overall this study illustrated the importance of continued omega 3 supplements to maintain reduction in cardiometabolic markers, seen by young adults taking daily fish oil supplementation and that genotype may be a potential mediator of an individual’s response to fish oil supplements, particularly with regard to EPA levels. Knowledge of an individuals FADS1/2 genotype may help to personalise long term strategies to improve health (and in this case especially cardiovascular health).
Personalised FADS1 Genetic Information And Motivation For Behaviour Change
Gillingham et al. cited by Roke et al. showed that in minor allele carriers (T), blood EPA levels increased to levels equivalent to those in the major (GG) allele carriers, when they were given dietary ALA, suggesting that providing individuals with their FADS genotype information, may be a good approach to encourage intake of Omega 3s and optimise dietary recommendations. Roke et al. went on to test the impact of providing personal genetic information for FADS1 on the consumption of Omega 3 FAs in a population of female adults over a 12-week period. Changes in EPA and DHA intake from foods and supplements were looked at, blood Omega 3 FA levels analysed and people’s perceptions of nutrition and genetics were assessed. Female adults (18-25 years) were recruited for the study and those regularly consuming omega 3 FA supplements and/or fish at least 2 times per week and those allergic to fish were excluded. 28 people were allocated to the genetic group and 29 to the non-genetic group, all of whom received the intended intervention. Participants were provided with generic information documents that provided information about Omega 3 FAs and an overview of the association between SNPs in FADS1 and omega 3 metabolism, in order to ensure that individuals had similar levels of knowledge. Individuals in the genetic group were told whether they were a major (GG) or minor (GT or TT) carrier and individuals in the non-genetic group only received this information at the end of the study. No dietary advice was provided in a genotype specific manner, as the main goal of the study was to assess whether or not individuals given their FADS1 genetic information adjusted their omega 3 dietary habits.
When compared to the control group, there was little evidence that providing personalised FADS1 genetic information affected EPA and DHA intake and circulating blood levels, however among individuals who had received their genetic information, compared to controls, there was a greater awareness of Omega 3 terminology, a less frequent rating that cost was a barrier to Omega 3 intake and they found their genetic info was useful in the context of generic nutritional info with regard to omega 3 FAs. Both groups increased their EPA and DHA dietary consumption, resulting in increased % EPAs in RBC, but more so in the minor allele carriers (59%) vs. major allele carriers (40%). Only 32% in the genetic group, compared to 61% in the non genetic group rated that ‘Omega 3 foods are expensive’ as being a barrier to intake, indicating that perhaps having genetic info can change attitudes about the value of healthy eating and with increased awareness and a lower perception that cost is a barrier to Omega 3 intake may result in individuals in this group being more likely to choose foods with omega 3 FAs going forward. Limitations of this study should be noted which are the small sample size of this study with only female participants, aged 18-25 years, predominantly of Caucasian/European descent and who were well educated were included. Furthermore, the food frequency questionnaire assessed intake of EPA and DHA but not ALA.
Overall authors concluded that the provision of personalised FADS1 genetic information to young adults, might be an additional factor to motivate behaviour changes to increase consumption of Omega 3s.
Variations in the FADS1 and FADS2 gene cluster have been found to affect polyunsaturated fatty acid (PUFA) metabolism and have been associated with changes in blood concentrations of long chain PUFAs. SNPs in FADS1 and 2 have been associated with changes in lipid metabolism, cardiovascular disease and have also been associated with glucose metabolism, type 2 diabetes and CRP levels.
FADS1 rs174537 is one of the most common SNPs that has been researched and found to impact on PUFA metabolism. Individuals carrying the minor allele (TT or TG) have been found to have lower levels of AA and a lower risk of cardiovascular disease than major allele carriers (GG), who have been found to have increased AA levels and an increased risk of inflammation, cardiovascular disease and other conditions related to inflammation, in the presence of a Westernized diet where intake of LA is generally high.
Individuals carrying the minor allele for rs174537 tend to see greater improvements in changes in PUFA composition in response to omega 3 supplementation, compared to those carrying the GG genotype. This may indicate that Omega 3 recommendations may be influenced by variations in this SNP, and perhaps the major risk allele requires a higher Omega 3 intake, in conjunction with a reduced LA intake.
Foods that should be increased because they are rich in Omega 3s, EPA and DHA, include oily fish and foods rich in ALA include flaxseed and flaxseed oil, chia seeds, walnuts, soybean, tofu and edamame beans and seaweed, nori and spirulina. Food rich in LA, which should be reduced, include certain oils and fats commonly found in Westernized diet such as soybean, corn and palm oils, margarine and shortenings and products containing these foods (e.g. many processed and convenience foods).
It should be noted that for sustained benefits, dietary changes should be adopted as an ongoing lifestyle approach e.g. when recommended, increased intake of Omega 3 fatty acids should be continued as benefits may be lost on cessation of this increased intake/ supplement. The same may apply for reduced intake of LA, that this needs to be an ongoing lifelong recommendation rather than something that is done for a short period only to get levels to return to normal.
Furthermore, providing individuals with their genetic information and explaining what this means and the risks involved, may improve compliance to recommended intake and reduce perceptions of the barriers involved.
Many of the studies looked at had small sample groups and further studies are needed before specific recommendations on amounts of Omega 3s required for each SNP can be provided.
Diet-Gene Interactions and PUFA Metabolism: A Potential Contributor to Health Disparities and Human Diseases.