Nuts, seeds, and plant oil intake may lower death risk

  • The human body needs a variety of nutrients, including those that come from fat.
  • Alpha-linolenic acid (ALA) is an omega-3 fatty acid that the body needs. The body does not make it, so people have to obtain it through diet. It mostly comes from plant-based sources.
  • Research suggests that dietary intake of ALA may decrease overall mortality risk.

Fat is an essential macronutrient that the body needs to function. Many foods contain different types of fat. One type of nutrient people get from eating certain types of fat is omega-3 fatty acids. ALA is the primary omega-3 fatty acid that comes from plant sources.

A recent study published in the BMJ found that diets with higher levels of ALA had associations with overall lower mortality risk.

Fat consumption and ALA

Like all living creatures, humans need certain nutrients to survive. There are some nutrients that the body cannot produce on its own, so people need to obtain them through diet.

The recommendations about the types and amounts of fat people need are constantly changing as new data emerge.

The National Institute of Health Office of Dietary Supplements notes that omega-3 fatty acids are nutrients that mostly come from plant-based food sources. The body uses omega-3 fatty acids for several purposes, including as an energy source and maintaining its cells’ structure.

According to the American Heart Association, omega-3 fatty acids come from polyunsaturated fat sources, including plant-based oils, nuts, and seeds. Sources of polyunsaturated fats include:

  • soybeans
  • canola oil
  • walnuts
  • flaxseed

All of these contain ALA. The American Heart Association recommends that people get most of their dietary fat from polyunsaturated sources of fat, further making ALA an essential component of the diet.

Nutrition expert, dietitian, and researcher, Dr. Anastasia Kalea explained it this way to MNT:

“Alpha-linolenic acid (ALA) is an essential plant-based essential omega-3 polyunsaturated fatty acid that must be obtained through the diet, as we cannot synthesize it in our bodies. Good sources of ALA are several seeds, seed oils, and nuts. For example, flaxseeds (linseeds) and their oil typically contain 45–55% of fatty acids as α-linolenic acid, while soybean and rapeseed oil and walnuts contain 5–10% of fatty acids as ALA. Corn oil and sunflower oil are poor sources of ALA.”

Researchers continue to study the intake of ALA and its associated health benefits, including how it impacts overall mortality.

ALA and decreased mortality rate

The new research is a systematic review and dose-response meta-analysis. Researchers included 41 different studies in their analysis. For inclusion in the meta-analysis, the study had to be a prospective one of adult participants that examined the risk association between ALA and mortality.

This meta-analysis looked at all-cause mortality, cardiovascular disease mortality, coronary heart disease mortality, and cancer mortality. The researchers looked at both dietary intake for ALA and blood levels of ALA. In her review of the study’s findings, Dr. Kalea noted this element to be particularly unique. She told MNT:

“What makes this study interesting is the fact that the researchers did not look [at] the dietary intake of ALA only, which comes with its own set of biases and limitations, but looked at blood, serum, and adipose tissue levels of ALA — a more objective tool to assess ALA status. They also looked at the dose-response association between intake of ALA and risk of mortality, which was nice to see.”

Researchers found several significant results when comparing high ALA dietary intake with low dietary ALA intake.

Overall, high ALA intake was associated with a lower risk for death from all causes. It was also associated with lower mortality risk from cardiovascular disease and coronary heart disease.

The researchers specifically note in their findings that: “Each 1 gram per day increment in ALA intake was associated with a 5% lower risk of CVD [cardiovascular disease] mortality.”

However, they found a slightly increased cancer mortality risk associated with high ALA dietary intake. Dr. Kalea noted that there could be a few different reasons for this and offered her recommendations for further research in this area.

“Perhaps before going toward the recommendation that a high intake of ALA may be associated with a slightly increased risk of cancer mortality, we need to conduct studies with the appropriate study design to address this question.”

“This study may fall into classification biases, as this finding is based on the analyses of the highest versus lowest intakes, which is problematic for many reasons. The key one is that the dietary intake was recorded using food frequency questionnaires as a tool to [try to] trace intake of a food component consumed in low quantity in the diet to begin with. Furthermore, these low vs. high intake differences were not reflected in tissue biomarkers of ALA.”

In terms of blood levels of ALA, researchers found that higher levels of ALA were only associated with lower risk for overall mortality and coronary heart disease mortality. They did not find any significant association between ALA blood levels and cancer mortality.

Overall, results indicate potential benefits of ALA intake and a need for continued research regarding recommended levels of ALA intake.

Study limitations and continued research

The study did have limitations. The studies included in the analysis were observational. This means that they cannot determine a causal relationship between ALA and mortality. There is also the possibility of missed factors that may have influenced the examined studies’ results. Errors in the measurements of food and nutrients were possible as well.

The analyzed studies showed mixed results, possibly due to differences in follow-up time frames, ALA intake, and the frequency of dietary assessments. Finally, most of the studies did one estimate of ALA intake taken at the beginning of the study, therefore not accounting for changes people might have made to their intakes during the follow-up.

Dietitian and nutrition expert Kristin Kirkpatrick noted that it is also critical to look at the wider context of the study’s information. This includes looking at the sources of food and how these foods provide multiple benefits. She explained to MNT:

“I think this study outlines an important factor in nutritional science — we cannot always isolate a certain macronutrient, vitamin, or mineral; we also need to assess the food [that delivers it]. Plant-based diets have been successful in many of my patients in terms of benefits to metabolic health and sustainability. I counsel these patients to look toward whole foods sources, such as walnuts, whole soy sources, and flaxseed. In addition to this, I look at their ratio of omega 3’s and omega 6 sources as well.”

Dr. Kalea also noted that the “Findings from this paper on the effects of plant-based ALA on all-cause mortality support the importance of consuming a healthy, balanced, varied, plant-based diet. Focusing on one food component and its functions alone perhaps distracts us from looking at the beneficial synergistic effects of many nutrients present in our diets.”

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