For the flaxseed fans
Although the term “functional food” is loosely defined in the wide, vacillating, and often conflicting field of nutrition science, flaxseed has been coined a “functional food” - a nutritional item that, besides offering energy and nutrients, also offers other health benefits. With this definition, most naturally-occurring foods can be considered functional. Food can (and does) actually act as medicine, meaning what we ingest is capable of both preventing and treating disease or ill-health.
Flaxseed specifically has been studied for its ability to prevent disease. It is frequently cited as a superfood that contains numerous health-promoting compounds, and it is thought to be a beneficial addition to smoothies, yogurt parfaits, baked goods, and overnight oats. How has flaxseed earned its reputation? And is its hype justified? Keep reading for a spotlight on flaxseed.
What is flaxseed?
Unsurprisingly, flaxseed is a seed that comes from the flax plant. Like other seeds, it contains a moderate amount of protein and fat, in addition to a substantial quantity of fiber per serving. Its high fiber content is likely why it has been used to improve digestion for centuries.
What are its health-promoting compounds?
Fiber
Just a tablespoon of ground flaxseed contains 3 grams of fiber. Approximately one-third of this is soluble fiber, and the other two-thirds are insoluble fiber. Why is fiber beneficial?
*Remembering that the gut contains its own complex neural network called the enteric nervous system will enhance your digestion (pun intended) of this section, as well keeping in mind the constant crosstalk between the brain and the gut.
**Also remind yourself of the numerous signaling cascades that can occur from the hormonal activation of any one receptor, depending on various contexts like cell type, secondary messengers, etc. (The human body is SO complex and cool!)
Satiety
Fiber slows digestion by slowing gastric emptying, slowing nutrient absorption, and increasing gastric distention.¹ This contributes to increased satiety, making you feel full longer, via both mechanical/physical and biochemical/hormonal mechanisms.
Increased stool bulk
Soluble fiber forms a gel in the intestinal tract, and soluble fibers with high viscosity are thought to be responsible for the cholesterol-lowering and blood-glucose-lowering effects of fiber.¹ Insoluble fibers, on the other hand, add bulk to the stool.
Lowered blood glucose and increased insulin sensitivity
By decreasing the rate of digestion, the fiber in flaxseed can prevent blood sugar spikes. It also triggers the release of GLP-1 and PYY in the intestine, lowering blood glucose levels and increasing feelings of fullness, for hours after a meal. GLP-1 communicates not only with your pancreas to stimulate insulin, but also with your brain regarding hunger levels and satiety.² Similarly, PYY decreases food intake via communication with the brain (likely by inhibition of NPY neurons), while also acting as an antimicrobial (AMP) that regulates fungal balance and commensalism in the gut microbiome.³
Lowered cholesterol
Soluble fiber traps cholesterol in the intestines so it cannot be reabsorbed back into the bloodstream.
When fermented by bacteria that make up the gut microbiota, short-chain fatty acids (SCFAs) are produced, which negatively feedback on the synthesis of cholesterol in the liver. This is also why certain microbes or fecal bacterial signatures may be associated with increased or lowered risk of hypercholesterolemia.⁴
Microbiome nourishment
Fiber gets fermented by the microbes inhabiting the large intestine of the human digestive tract. This leads to the production of beneficial metabolites, which create a variety of physiological and metabolic changes (i.e. SCFAs). It is thought that the reduction in fiber consumption and the subsequent loss of microbiota diversity has contributed to the rise in obesity, type 2 diabetes, and other metabolic syndromes.⁵
Lignans
Lignans are polyphenolic compounds, as well as phytoestrogens. Flaxseed is the richest dietary source of lignans, with 85 mg per ounce.⁶ The bioavailabity of the lignans is increased when the flaxseed is ground or milled as opposed to whole. Why care about lignans?
Estrogenic or anti-estrogenic
Phytoestrogens can bind to estrogen receptors, thereby mimicking the signaling cascades endogenous estrogen can cause. Phytoestrogens may also act antagonistically by blocking estrogen receptors from binding endogenous estrogen. However, most phytoestrogens are much weaker than endogenous estrogens. What causes a phytoestrogen to be estrogenic or anti-estrogenic is still being studied, and depending on the biological tissue, one effect may be more beneficial than the other (i.e. estrogenic activity in bone to maintain bone mineral density).⁶
Anti-inflammatory
Lignans have been shown to inhibit inflammatory molecules, such as NF-kB.⁷
Antioxidant properties
Lignans have been shown to upregulate the expression of SOD and CAT, as well as other antioxidant proteins.⁷
Omega-3 fatty acids
Flaxseed is a rich source of ALA, which is a plant-based omega-3 fatty acid. It is thought that the standard American diet (SAD) is too high in omega-6 fatty acids and too low in omega-3 fatty acids (which are most often obtained through marine dietary sources, such as fatty fish, but can also be found in plants as ALA).
Anti-inflammatory
Omega-3 supplementation is associated with decreased levels of C-reactive protein (CRP), which is a marker of inflammation in the body.⁸
Omega-3s produce anti-inflammatory compounds, such as SPMs.
Given the role that inflammation plays in cardiovascular disease, autoimmune disease, and neurodegenerative diseases, omega-3 fatty acids are thought to play a role in preventing multiple diseases and improving multiple facets of health and well-being. Omega-3 fatty acids are associated with a reduced risk of CVD, cancer, depression, cognitive decline, macular degeneration, and rheumatoid arthritis, amongst other things.⁹
Why should I care?
Lower risk of cancer
Flaxseed can inhibit cellular proliferation and angiogenesis (i.e. tumor growth).¹⁰
The estrogenic properties of flaxseed may play a role in its ability to lower the risk of estrogen-associated cancers, such as breast cancer.¹⁰
Improved digestion & GI health
The fiber in flaxseed can stimulate digestion.
Flaxseed can positively modulate the gut microbiome, leading to a variety of physiological effects, ranging from increased SCFAs and lowered cholesterol, to better glycemic control, and more.
Lowered risk of cardiovascular disease
Omega-3 fatty acids lower the risk of CVD.
Fiber can lower cholesterol.
Lowered risk of diabetes, obesity, and metabolic syndromes
The fiber in flaxseed can impact intestinal hormone secretion, thereby impacting blood glucose levels. It can also modulate the microbiome, which is strongly associated with obesity and metabolic disease.¹¹
The metrics we use to analyze food can never fully account for the myriad of cascading effects any compound can have on human physiology. The more I learn about any food item - or even any singular component of one food item - the more astounded I am at the complexity and interconnectedness of the human body. At the end of the day, we literally are what we eat on a biochemical level, and as science continues to elucidate the mechanisms by which food impacts physiological systems, all we can do is listen to our bodies, which communicate with our logical-thinking brains constantly. Sometimes, categorization and definitions fail us, like when considering the fluctuating spectrum between health and disease, and all the factors that play into where we fall on this spectrum on any given day.
Future blog posts will examine the metric of calories and other components of the caloric expenditure equation, as well as mycorrhizal relationships that can impact nutrient content and the flavor profile of plants.
Bibliography
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Karra E, Chandarana K, Batterham RL. The role of peptide YY in appetite regulation and obesity. J Physiol. 2009;587(1):19-25. doi:10.1113/jphysiol.2008.164269
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