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Dietary Intervention with Fish Oil: Effect on Lipid Profile and Blood Pressure

Paper Type: Free Essay Subject: Nutrition
Wordcount: 4453 words Published: 18th May 2020

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A Dietary Intervention with Fish Oil: To See the Effect on Lipid Profile and Blood Pressure in Healthy Individuals.

Amy Bertham – 17035657




This study measured the effect of fish oil supplementation on15 healthy individual’s lipid profiles (including HDLc, LDLc, total cholesterol and triglyceride) and blood pressure (systolic and diastolic pressure).  The results from this study suggested that the only significant change after the two-week intervention was a reduction in triglyceride levels.  There were no significant differences in other lipid profile levels that were tested (HDLc, LDLc and total cholesterol), nor in blood pressure measurements at the conclusion of the intervention.  Overall, these results do not support the hypothesis that a daily dose of fish oil lowers LDL, improves the total blood lipid profile and decreases blood pressure and overall lead to a reduction in cardiovascular disease risk. 


Fish is the richest dietary source of omega 3 long chain polyunsaturated fatty acids, which have been extensively researched for their health benefits.  There have been many reports that shows how the potential supplementation of fish oil can lower blood triglyceride levels, reduce blood pressure and improve blood lipid status (Lectures). 

Fish oil is the most commonly consumed dietary supplements, possibly due to being rich in omega 3 fatty acids.  Research suggests that fish oil may reduce some risks associated with heart disease (Kris-Etherton, Harris & Appel. 2002).  Fish oil also has a strong anti-inflammatory effect and can help reduce symptoms of inflammatory diseases, especially rheumatoid arthritis (Kris-Etherton, Harris & Appel. 2002).  

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A favorable lipid profile is typically lower in triglycerides, cholesterol, low-density lipoproteins (LDLc) and high-density lipoproteins (HDLc).  Omega three and omega six fatty acids represent two classes of polyunsaturated fatty acids that derive from linoleic acid and alpha-linolenic acid.  Omega 3’s are composed of two crucial components; eicosatetraenoic acid (EPA) and Docosahexaenoic acid (DHA).  EPA and DHA are highly unsaturated fats and help reduce inflammation and the risk of chronic diseases such as heart disease (Lectures)

Western diets are generally more abundant in omega 6 fatty acids.  These are that are found mainly in vegetable oils (such as canola oil, linseed oil, soybean oil and walnut oil) which are rich in linoleic acid. Too much omega 6 can be dangerous, as it can cause your blood pressure to raise, lead to blood clots that can cause heart attack and stroke and can cause your body to retain water.  It can also trigger the body to produce pro-inflammatory chemicals.  Omega 3 fatty acids, however, have been documented to positively influence the risk of cardiovascular disease (Kris-Etherton, Harris $ Appel, 2003).  Finally, there are many benefits of EPA and DHA relating to their capacity to alter numerous physiological pathways and cardiovascular risk (Mori, T. 2017).  The human body is unable to convert omega 6 or omega 3 fatty acids and have a very limited capability to convert alpha-linolenic acid to EPA and DHA, therefore it is important to ensure their inclusion within a healthy diet.  One of the main dietary sources of EPA and DHA are fish especially oily fish. 

CVD is one of the most common chronic human disease in the world and has constituted the leading cause of morbidity and mortality globally.  It has been advocated for many years that reducing dietary saturated fat (SFA) intake and replacing it with polyunsaturated fats can be a beneficial dietary strategy to prevent CVD.  This is due to the anti-inflammatory properties of a polyunsaturated fat.  Long chain PUFA’s mainly omega 6 and omega 3, especially EPA and DHA have been extensively reported to play roles in reducing plasma lipid and arterial lipoprotein lipase levels, macrophages numbers and atherosclerosis (Kris-Etherton, Harris & Appel. 2002). 

Therefore, in this study we aim to investigate the effect of supplementation of fish oil capsules on lipid profiles and other health markers associated with the risk of CVD in healthy individuals.  We hypothesize that a daily dose of fish oil will lower LDL cholesterol, improve the blood lipid profile and decrease blood pressure. 



  1. Lancing device – Accu-Chex
  2. MediSense Optimum Sensor – FreeStyle Optimum Neo
  3. MediSense Optimum Blood Glucose Electrode – Blood Glucose Testing Strip (Abbott Diabetes Care Ltd)
  4. Blood Pressure – Sphygmomanometer
  5. Blood lipids – Cardio check
  6. Dietary Intake – Food scales and 3-7 day weighted food records


We studied 15 healthy individuals (4 males and 11 females) aged 25 ± 7.37 years (mean ± standard deviation) who were recruited from a third-year nutrition class at Massey University.  All participants had normal blood lipids at baseline.  The subjects were non-smokers, however there were five individuals who indicated they regularly consume alcohol.  Two of these individuals drink more than 6 standard alcoholic drinks per week.   Participants agreed that they would not actively try to lose weight during the two week intervention period.  14 of the 15 subjects were moderately active and were asked to maintain their same level of physical activity during the study.  Of the 15 participants, 3 indicated they followed a pescatarian diet and 1 indicated they were vegan. 

Prior to the beginning of the study each participant was required to complete a food diary, in which they weighed their food for three days.  The food diary entries were then entered into food works.  Food Works is a computer program designed to simplify the process of nutrient analysis.  Each individuals diet was analyzed by food works to give an accurate representation of each individuals energy intake as well as the percentage of energy from carbohydrate, fats (saturated fats) and proteins.  Tis program also provided an average amount of omega 6 and omega 3 each individual consumed on a daily basis.

Each participant also completed questionnaire prior to the dietary intervention.  This is due to the fact that the food dairies were only kept for a three-day period and therefore may not be an accurate reflection of all the foods that the participants are consuming.  From the results of both the food diary and the survey, it appears there was only one participant currently consuming oily fish more than once per week. 

Baseline measurements of both blood pressure and lipid profiles were taken. Participants were then given fish oil supplements to take over a two-week period.  During the last three days of the study participants completed an additional weighed food diary. 

After the completion of the two-week study, tests were repeated to see if there were any significant changes in individual’s blood pressure and lipid profiles.  Weight and hip/waist circumference were also remeasured to ensure that each participant had maintained a steady weight. 

The baseline tests that were taken were an initial blood glucose reading, a cardio check to measure blood lipids and a sphygmomanometer to take blood pressure readings.  The lipid test and blood glucose levels were measure using a finger prick (using the lacing device, Accu-Chex), then blood glucose was measured using the MediSense Optimum Sensor (freeStyle Optimum Neo) and the MediSense Optimum Blood Glucose Electrode (Blood Glucose Testing Strip). 



The results from this study suggested that the only significant change after the two-week intervention was the reduction in triglyceride levels.  The other lipid profile tests that were conducted, the HDLc, LDLc and total cholesterol did not have significant change.  The blood pressure (both systolic and diastolic) also did not show significantly change during the two-week intervention. 

Participants reported adhering to the intervention protocols over the two-week intervention period in that each day over the two-week period participants took one fish oil supplement.   

Table One: Lipid Panel Results

Before Intervention

After Intervention

% Difference


Total Cholesterol (TC)

 4.25 ± 0.04

4.58 ± 1.05



LDL Cholesterol

2.22 ± 1.30

2.51 ± 1.11



HDL Cholesterol

1.60 ± 0.44

1.65 ± 0.45




2.80 ± 1.18

2.97 ± 1.15




0.79 ± 0.27

0.65 ± 0.11



Systolic Blood Pressure

115.60 ± 10.83

113.80 ± 11.45



Diastolic Blood Pressure

74.53 ± 6.48

73.87 ± 7.64



Note: Results are fasting values.  The values are the mean ± standard deviation


Table Two: Food Works Results


Before Intervention

After Intervention

% Difference

P Value

Total Energy

8087.75  +/-  1917.68

7609.65 +/-  1860.40



% Energy from Carbohydrates

41.63 +/- 6.48

43.21 +/-  5.91



% Energy from Protein

18.67 +/- 4.36

19.12 +/-  4.03



% Energy from Fat

33.90 +/- 6.97

32.53 +/-  5.83



% Energy from Saturated Fat

12.59 +/- 5.29

10.97 +/-  4.01



Omega 3

0.06 +/- 0.1

0.38 +/-  0.36



Omega 6

7.50 +/- 5.80

7.73 +/-  4.89



Note: These values are based on weighed food records and foodworks analysis.  The values are the mean ± standard deviation

The results in table 1 shows the changes in lipid blood panels from before the dietary intervention (baseline results) and after the intervention.  There was only a significant change in the triglyceride levels after the two-week supplementation of fish oil. 

The results in table 2 shows the food works output and shows that other than the fish oil supplementation, there was no significant change in the participants eating habits during the study, with the exception of the fish oil supplement. 


In this study we aimed to answer whether a daily dose of fish oil would lower LDL, improve the blood lipid profile and decrease blood pressure, leading to an overall reduction in cardiovascular disease risk.  We found that the only significant improvement to the lipid profile was a decrease in the triglyceride levels.  This does not completely support our full hypothesis. 

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The results from this study suggest that triglyceride levels may be reduced through the use of fish oil supplementation.  This is important as reduced triglyceride levels results in the reduction of cardiovascular risk (Kris-Etherton, Harris and Appel. 2002).  It’s believed that omega 3, as found in fish oil, decreases triglycerides through the rduction of plasma triglycerides through the rate of VLDL synthesis in the liver (Shearer, Savinova & Harris, 2012).  Triglycerides are transported through the body by all classes of lipoproteins particles, with very low-density lipoproteins (VLDL) and chylomicrons.  Research has shown that omega 3 fatty acids can lower plasma triglycerides.  The triglycerides lowering effect of EPA and DHA has been demonstrated in numerous trials, when 3-4g of omega 3 FA’s can decrease plasma triglycerides by 30% (Shearer, Savinova & Harris, 2012)

Research has shown that fish oil may result in improvements in HDL cholesterol status and a decrease in LDL cholesterol.  The results from our study showed no significant changes in the HDL cholesterol and LDL cholesterol levels.  This may be due to the fact this study was conducted over a two-week time frame, and it may take longer to see the true impact of fish oil supplementation on HDL and LDL cholesterol levels.

Research has shown that fish oil has a positive effect HDL cholesterol by lowering it.  This is because fish oil can effect the HDL metabolism by reducing the activity of cholesterol ester transfer protein, which transfers cholesterol esters from HDLs to VLDL and LDLs, largely in the exchange of VLDL triglycerides.  This causes a reduction in the triglyceride’s (Nestel, P. 2000). 

The effects of fish oil on LDL metabolism, changes in LDL particles are minor, but tend towards larger, cholesterol-enriched LDLs.   The LDL cholesterol is susceptible to oxidation. 

There are some potential downsides to supplementation with fish oil.  Fish oils oxidize readily, forming primary and secondary oxidation products, which may be harmful for humans (Nestel, P. 2000).  Some recent studies have reported that fish oil supplements in Australasia are oxidized above acceptable international limits, however other studies reported low levels of oxidation (Heller, Gemming, Tang & Grant. 2019).  A study conducted by Heller, Gemming, Tung and Grant (2019) tested 26 supplements of which 38% exceeded the limit of primary oxidation, 25% exceeded the limit of secondary oxidation and 33% exceeded the limit for total oxidation, according to international recommendations (Heller, Gemming, Tung & Grant. 2019).  Oxidation of omega 3 fatty acids is complex and the degree and rate of oxidation can be influenced by many factors.  The initial stage of oxidation of fish oils leads to increased levels of hydroperoxides, which decompose into a variety of radicals.  These can react with unoxidized PUFA to form additional hydroperoxides, while also breaking down to form a wide range of possible secondary oxidation products (Cameron-Smith, Albert & Cutfield. 2015). 

Omega 3 fatty acids have been shown to reduce systolic blood pressure by 2.1 mmHg and diastolic blood pressure by 1.6 mmHg in a study conducted by Geleiinse et al (year).  In another study conducted by Morris et al. found significant reduction in blood pressure of 2.0 – 3.4 mmHg in studies where subjects who consumed 5-6g/d of omega 3 FA.  Likewise, Appel et al found that blood pressure was decreased by 3.5 – 5.5 mmHg in a trail where subjects were given >3g/d of omega 3 FA.  In this study they found that DHA seemed to be more effective than EPA in the lowering of blood pressure.  These results were not reflected in our study as the systolic and diastolic pressure did not significantly change throughout the experiment.  This difference may again be due to the differing lengths of supplementation used in the aforementioned studies when compared with our study.

In the study the total cholesterol to high density lipoprotein (HDL) ratio did not change significantly.  The ratio is important in the determination of a patient’s potential risk of developing heart disease in the future, the optimal ratio is 3.5:1 (Real, et. al.).  In the study conducted by Ciubotaru, Lee & Wander (2003) participants were given 7g of fish oil daily, this had a significant effect on the total cholesterol and HDL ratio, this indicates that the fish oil can be useful in the reduction of this ratio.  This study was conducted over five weeks, therefore, in comparison to the length of this study, it indicated that it might take a longer period of time to see the true impact of fish oil on this ratio.

In our study participants were given Blackmores 1000mg fish oil capsule (Blackmores, NZ).  Many fish oil capsules advertise that the contain 1000 mg of fish oil.  However, since natural fish oils typically contain just 30% EPA and DHA combined which means that there is only 300mg of EPA/DHA per capsule that can be readily absorbed (Raatz, et. al). 

If this study was to be conducted again, it would be useful to conduct it over a longer length of time, as in comparison to similar research studies where positive results were found in studies conducted over at least a month.  It could also be beneficial to split participants into two groups, giving each group a different amount of fish oil to see if the amount of fish oil taken has an effect on the change to the blood pressure and lipid profile of an individual.  This study has a number of limitations, including its short duration and small sample size.  Despite these limitations there was one significant reduction in the triglyceride levels after a fish oil supplementation. 

The results from this study suggest that triglyceride levels may be reduced through the use of fish oil supplementation but none of the other lipid profile results we expected to see changes/improvement in did not occur.  Also, blood pressure did not have any significant changes.  If further research was to be done in the future it would be useful to look further into fish oils effect on cholesterol and blood pressure, by conducting a longer study.  Doctors could use this study as an indication that over small period of time fish oil can successfully reduce triglyceride levels.  This could help with the reducing the risk of cardiovascular disease. 


This study measured the effect of fish oil supplementation on15 healthy individual’s lipid profile and blood pressure.  The results from this study suggested that the only significant change after the two-week intervention was the reduction in triglyceride levels.  The other lipid profile tests that were conducted, the HDLc, LDLc and total cholesterol did not have significant change.  The blood pressure (both systolic and diastolic) did also not significantly change during the two-week intervention.  These results do not support our hypothesis that a daily dose of fish oil would lower LDL, improve the blood lipid profile and decrease blood pressure which could reduce cardiovascular disease risk.  Results are promising for the use of fish oil supplementation in decreasing triglyceride levels.  Future research could extend upon these findings by exploring the amount of supplementation needed to gain the greatest results. 






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