Fish or Soy?

Summarized by Robert W. Griffith, MD
June 17, 2005

Introduction

Omega-3 fatty acids are polyunsaturated fatty acids (PUFAs) that are effective in preventing or reducing the rate of sudden death in healthy men - to achieve this, however, they have to eat at least one meal of fish a week. People with coronary heart disease taking omega-3 supplements has a similar benefit. Cardiologists think their main effect may be a decrease in the risk of heart irregularities (arrhythmias), which is achieved by an increase in heart rate variability (HRV).¹ Having a relatively high HRV is an indicator of the heart's ability to respond to outside circumstances, and is a sign of heart health.

A group of US and Mexican scientists decided to study the effects of long-term fish-oil omega-3 fatty acids supplementation on HRV in older persons, and compare them with the possible benefits of soy - namely the plant-derived omega-3 fatty acids contained in soy oil. There have been several reports on the hidden benefits of soy consumption, but they haven't been compared with fish-derived omega-3 before. The results of the study are published in the journal Chest, and we summarize them here.

What was done

Fifty-eight volunteers from a Mexican nursing home were allocated randomly to take either 2 grams of fish oil capsules or 2 grams of soy oil capsules, daily, for 6 months. Participants had to be over 60, without a pacemaker, have no cardiac irregularities, and not be taking anticoagulants (except aspirin).

The participants had their heart rate measured over a 6-minute period while they were lying down, on alternate days for a 2-month baseline period. This allowed an HRV baseline value to be determined for each participant. The heart rate measurements were continued on alternate days throughout the 6 months of the study.

All participants also provided information on their medical history, medication use, and completed a food-frequency questionnaire.

What the study showed

There were 26 participants in each supplement group. Their average age was 76, and just over half were women. One in 8 of them smoked. Six participants didn't complete the study, leaving 52 for full analysis.

There were 1,860 actual HRV assessments done during the 2-month baseline and 6-month supplementation periods. In both supplement groups, the average HRV measurements increased significantly overall during the supplementation period, compared to baseline. With fish oil, the increase was significant over the first 6 weeks, as well as for the rest of the 6-month period, whereas the soy-oil participants only had significant improvements after 18 weeks. Moreover, after adjusting for individual age differences and average heart rates, the fish-oil group increased their HRV measurements to a greater extent than those in the soy-oil group.

Both supplements were well tolerated by the participants; however, 41% of the fish-oil group reported belching, compared with 16% of the soy-oil group, while 12.5% of the fish-oil and 8% of the soy-oil groups reported having nausea at some time during the 6 months.

The food questionnaires showed that the average consumption of dietary omega-3 fatty acids was poor - only 9% of both groups ate fish other than tuna.

What this study means

Fish-oil supplements were superior and quicker in increasing HRV than soy-oil supplements, when given in equal amounts. A reduced HRV predicts mortality and heart irregularities, so that increasing it is a desirable step. In this respect, the benefits of soy are inferior to those of fish-oil supplements. This must be set against slightly greater side-effects with fish oil (belching, nausea). Assuming they have a need to take omega-3 fatty acid supplements (because of low dietary intake), the consumer should make the choice: more effective and more side effects vs. less effective and fewer side effects. In fact, any benefits of soy consumption can be readily compensated for by taking a fish-oil supplement.

Source

• Cardiac autonomic changes associated with fish oil vs soy oil supplementation in the elderly. F. Holguin, M. Tellez-Rojo, M. Lazo,  et al., Chest, 2005, vol. 165, pp. 1102--1107
  
  

Footnotes
1. HRV is a measure of the regulation of the natural pacemaker of the heart - the sinoatrial node - by the nerves controlling it. The beat-to-beat changes in the rhythm of the heart provide an indirect measure of heart health, shown by the balance between sympathetic and vagus nerve activity.

Related Links
Eat More Fish for Irregular Heartbeat?
Soy and Heart Disease
Linolenic Acid Intake Linked to Heart Health

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