Lignans may reduce diabetes risk
By David Dunaief, M.D.
Type 2 diabetes is pervasive throughout the population, regardless of age. Yet, even with its prevalence, many myths persist about managing diabetes. Among these are: Fruit should be limited or avoided; soy has detrimental effects with diabetes; plant fiber provides too many carbohydrates; and bariatric surgery is an alternative to lifestyle changes.
All of these statements are false. Let’s look at the evidence.
Fruit, whether whole fruit or fruit juice, has been thought of as taboo for those with diabetes. This is only partially true. Yes, fruit juice should be avoided because it does raise or spike glucose (sugar) levels. The same does not hold true for whole fruit. Studies have demonstrated that patients with diabetes don’t experience a spike in sugar levels whether they limit the number of fruits consumed or have an abundance of fruit (1). In another study, whole fruit was shown to reduce the risk of type 2 diabetes (2).
In yet another study, researchers looked at the impacts of different whole fruits on glucose levels. They found that berries reduced glucose levels the most, but even bananas and grapes reduced these levels (3). That’s right, bananas and grapes, two fruits people associate with spiking sugar levels and increasing carbohydrate load. The only fruit that seemed to have a mildly negative impact on sugars was cantaloupe.
Whole fruit is not synonymous with sugar. One of the reasons for the beneficial effect is the flavonoids, or plant micronutrients, but another is the fiber.
In the Nurses’ Health Study and NHS II, two very large prospective observational studies, plant fiber was shown to help reduce the risk of type 2 diabetes (4). Researchers looked at lignans, a type of plant fiber, specifically examining the metabolites enterodiol and enterolactone. They found that patients with type 2 diabetes have substantially lower levels of these metabolites in their urine, compared to the control group without diabetes. There was a linear, or direct, relationship between the amount of metabolites and the reduction in risk for diabetes. The authors encourage patients to eat more of a plant-based diet to get this benefit.
Foods with lignans include flaxseed; sesame seeds; cruciferous vegetables, such as broccoli and cauliflower; and an assortment of fruits and grains (5). The researchers believe the effect is from antioxidant activity.
Soy and kidney function
In diabetes patients with nephropathy (kidney damage or disease), soy consumption showed improvements in kidney function (6). There were significant reductions in urinary creatinine levels and reductions of proteinuria (protein in the urine), both signs that the kidneys are beginning to function better.
This was a small, but randomized controlled trial over a four-year period with 41 participants. The control group’s diet consisted of 70 percent animal protein and 30 percent vegetable protein, while the treatment group’s consisted of 35 percent animal protein, 35 percent textured soy protein and 30 percent vegetable protein.
This is very important since diabetes patients are 20 to 40 times more likely to develop nephropathy than those without diabetes (7). It appears that soy protein may put substantially less stress on the kidneys than animal protein. However, those who have hypothyroidism should be cautious or avoid soy since it may suppress thyroid functioning.
In recent years, bariatric surgery has grown in prevalence for treating severely obese (BMI>35 kg/m²) and obese (BMI >30 kg/m²) diabetes patients. In a meta-analysis of bariatric surgery involving 16 RCTs and observational studies, the procedure illustrated better results than conventional medicines over a 17-month follow-up period in treating HbA1C (three-month blood glucose measure), fasting blood glucose and weight loss (8). During this time period, 72 percent of those patients treated with bariatric surgery went into diabetes remission and had significant weight loss.
However, after 10 years without proper management involving lifestyle changes, only 36 percent remained in remission with diabetes, and a significant number regained weight. Thus, whether one chooses bariatric surgery or not, altering diet and exercise are critical to maintain long-term benefits.
There is still a lot to be learned with diabetes, but our understanding of how to manage lifestyle modifications, specifically diet, is becoming clearer. The take-home message is: focus on a plant-based diet focused on fruits, vegetables, beans and legumes. And if you choose a medical approach, bariatric surgery is a viable option, but don’t forget that you need to make significant lifestyle changes to accompany the surgery.
(1) Nutr J. 2013 Mar. 5;12:29. (2) Am J Clin Nutr. 2012 Apr.;95:925-933. (3) BMJ online 2013 Aug. 29. (4) Diabetes Care. online 2014 Feb. 18. (5) Br J Nutr. 2005;93:393–402. (6) Diabetes Care. 2008;31:648-654. (7) N Engl J Med. 1993;328:1676–1685. (8) Obes Surg. 2014;24:437-455.
Dr. Dunaief is a speaker, author and local lifestyle medicine physician focusing on the integration of medicine, nutrition, fitness and stress management.