Although animal studies have demonstrated that dietary omega-3s lessen insulin resistance, human studies have yet to show consistent results. But before deciding whether omega-3s benefit human health or not, it’s important to understand some of the shortcomings of the research that make it challenging to draw definitive conclusions, or even compare studies with one another.
For example, most studies rely on dietary recall, a notoriously inaccurate methodology. Participants, who generally recognize fish as a healthy choice, may naturally overestimate their fish consumption.
Even if participants do accurately recall how much fish they ate over a certain amount of time, perhaps 6 ounces a week, estimating the true quantity of omega-3s they obtained depends upon so many variables that it becomes impossible. Was the salmon they ate grown in a fish farm with a corn-based diet (high in omega-6, low in omega-3), or was it wild Pacific salmon? Did they eat 6 ounces of tuna in a can with water or with oil, which can absorb some of the nutrients? Additionally, in studies where researchers gave omega-3 supplements, did participants receive long-chain fatty acids (EPA and DHA), for which research has provided evidence that they reduce inflammation? Or did they receive alpha-linolenic acid (ACA), a shorter-chain fatty acid form, which has different effects? Were the supplements taken with food or on an empty stomach, which lowers absorbtion?
Assuming all study recipients received exactly 1000 mg of EPA and DHA throughout the study, can it also be confirmed that researchers obtained participants’ baseline omega-3 levels? If an individual already had high omega-3s, it might be expected that marginal effects are recorded. On the other hand, those who started with low omega-3s and received a supplement might show beneficial effects. However, if you average the results from these two examples, they tend to cancel one another and investigators may conclude that omega-3s don’t have a benefit for what they were studying.
Despite the challenges of studying the role of omega-3s in human health, the concept of biological plausibility offers a path forward. Do omega-3s offer the biologically feasible potential to cause beneficial effects on insulin resistance?
Yes, they do.
To understand the connection, you need to understand insulin resistance as a chronic condition, like arthritis, diabetes, and kidney disease. Science today has a much better understanding of chronic disease: Underlying inflammation drives its progression. Chronic inflammation (the upheaval of the immune system) has many causes, among them stress, exposure to environmental toxins, social isolation, and diet. The more inflammation present, the greater the burden of chronic disease. Scientists have shown that the composition of the Western diet promotes inflammation, and omega-3s have potent anti-inflammatory effects. If you accept the concept of biological plausibility, then it makes sense that the anti-inflammatory properties of omega-3s would have a beneficial effect on insulin metabolism.
The 100-millon-person scourge
During a meal, the pancreas releases insulin, which travels to the cells in your body allowing them to accept nutrients after a meal. Without insulin, those nutrients—fats, sugars, amino acids from protein—cannot get into your cells.
Insulin resistance (not an absence of insulin) develops when the cells in your body don’t respond or are resistant to the action of insulin. It also affects movement of nutrients into cells. In response to insulin resistance, your pancreas releases more insulin to force the cells to absorb nutrients. The more insulin in your body, the more inflammation you create and the more weight you gain. The more inflammation you create and the more weight you gain, the more insulin resistant your cells become. This vicious cycle is very difficult to interrupt.
On the day that your pancreas produces as much insulin as it can, while still not being able to absorb those nutrients (they remain in the bloodstream, not absorbed in the cells), and the blood sugar reaches a certain level, you satisfy the criteria for a type 2 diabetes diagnosis. Remember, this didn’t happen overnight; the insulin resistance had been present for years. At least one-third of all Americans have insulin resistance, and before development of type 2 diabetes, years of insulin resistance causes:
- Abnormal lipids, such as high triglycerides
- Fatty liver, as reflected in your blood tests as an elevated ALT and AST
- Weight gain in the middle
- Accelerated aging, as reflected in shorter telomeres
So, how does insulin resistance occur? Out-of-control inflammation starts the cascade, and inflammation has many causes. For example, simply gaining weight causes more inflammation because excess fat cells produce inflammatory substances. Processed foods cause inflammation and often have a high content of omega-6 fatty acids which, in excess, also promote inflammation. Other important factors that promote inflammation include stress, depression, lack of exercise, and the natural reduction of the sex hormones estradiol and testosterone over time.
Put out the fire
The anti-inflammatory effects of omega-3s counter insulin resistance at the cellular level. They make your cells more sensitive to insulin so that you require less insulin to get the job done. The less insulin you have in your body after a meal, the less likely you are to gain weight and the less inflammation you have.
You can see that omega-3s play an important role, but still many questions still remain:
How much omega-3 should I take to reduce insulin resistance? Does it matter if I get my omega-3s from food or as a supplement? Is it possible to reverse type 2 diabetes by taking omega-3s?
As a physician with a passion for women’s health and the role that nutrition and supplements can play in preventing chronic conditions, I see the potential impact of omega-3s for my patients as promising and exciting. Clearly, the medical community needs more data, but first it must make the effort to fully understand the data that currently exists and the reasons behind some of the inconsistent findings and conflicting headlines that result.
Katherine Sherif, MD, is a professor and vice chair of the Department of Medicine at Thomas Jefferson University Hospital in Philadelphia, where she serves as director of Jefferson Women’s Primary Care.