The study under review suggests that incorporating chia seeds into the diet of older adults with well-controlled type 2 diabetes may facilitate weight loss compared to a mixture of oat bran and inulin. The degree of weight loss amounted to about 2.2% of initial bodyweight, which is close to the 3-5% weight loss likely to result in clinically meaningful reductions in metabolic risk factors.
An explanation for the superiority of chia seeds compared to the oat bran and inulin mixture is not clear. Although there was no self-reported difference in energy intake or macronutrients between groups, the greater weight loss in the chia seed group suggests that these records are not accurate. Chia seed fiber is insoluble, with a high water-binding capacity that makes it form a thick gel when mixed with liquids. Oat beta-glucan and inulin are both soluble fibers with a low viscosity. It has been previously demonstrated that chia seeds result in reduced appetite compared to flax seeds, another non-viscous fiber. Thus, there is a possibility that the chia group was more satiated and ate less food, regardless of what was being reported by the participants. Without measures of satiety and appetite, however, this remains speculation.
The weight loss observed in the study at hand becomes more difficult to interpret considering other published research. The authors of the current study had previously conducted a pilot trial in a similar population of older, overweight adults with well-controlled type 2 diabetes. The methodology and the way chia seeds were incorporated into the diets of the participants were also similar, except that only half the dose of chia was provided (15 grams per 1000 kcal) and it was compared to a wheat bran control. In this earlier study, there was no significant difference between groups in weight loss over 12 weeks.
Three other studies by independent labs have also found no effect of chia seeds on weight loss. Importantly, these studies involved overweight and obese adults without type 2 diabetes and lasted no longer than 12 weeks. One study provided 50 grams of whole chia seeds per day and compared it to a calorie- and macronutrient-matched control powder made from concentrated soy, sunflower oil, carrot fiber, and tapioca starch. Both supplements were to be consumed on an empty stomach before breakfast and dinner (25 grams at each) after sitting in water for ten minutes. In a follow-up to this study, researchers compared 25 grams of whole and ground chia seeds to a poppy seed control. Each serving was to be consumed as preferred by the participants so long as it was not heated in any way. The third study had participants consume 35 grams of chia flour per day or a wheat flour control, both of which were to be consumed as the participants preferred. None of these studies reported a significant difference in body weight between the chia seed group and the control.
Several important differences between all previous research and the study under review could explain why they failed to document a beneficial effect of chia seed consumption on bodyweight. The study at hand provided individualized nutrition counseling that included advice on how to incorporate the intervention products into the diet while maintaining an energy deficit. By contrast, the other studies just had people add the products into their diet. It could also be that weight loss differences required a larger sample size or longer study duration to be observed, both of which occurred in the study at hand. Finally, weight loss wasn’t statistically apparent in the study at hand until week 18; all other studies stopped after 12 weeks max.
Aside from changes in bodyweight, several other metabolic disease risk factors have been assessed in the available evidence discussed thus far. The pilot trial in adults with type 2 diabetes documented improvements in blood pressure and inflammation but not glycemic control. These findings were partially supported by the study at hand, which also observed reductions in inflammation but no changes in HbA1c or fasting glucose. The lack of change in glycemic control may be the result of concurrent medication use that masked any benefit, since both studies had at least half the participants using metformin alone or in combination with other glucose-lowering medications. The three independent studies found no benefit of chia supplementation on blood lipids, blood pressure, or inflammation when compared to the control. The discrepancy with the study at hand may be owed to the use of healthy adults rather than adults with type 2 diabetes.
This study was well-designed, with a randomized, double-blind structure and alternative fibrous control group helping to reduce potential bias. The length of the intervention also adds novelty to the findings, as all other trials up to now have been no longer than 12 weeks. However, the dropout rate was rather large and resulted in a study less powered than the researchers would have liked, meaning that all results should be taken with a grain of salt. Similarly, no adjustments for multiple comparisons were conducted, increasing the likelihood that some findings could potentially be the result of chance rather than the intervention.
It should also be noted that the lead author is a consultant for and has received money from a chia seed company and holds a patent on a viscous fiber blend for treating diabetes and metabolic syndrome. This in no way discredits the data, but it’s important to be aware of this information when drawing conclusions and comparing this study to other research.
Chia seed supplementation may result in greater weight loss than supplementing oat bran and inulin in adults with type 2 diabetes when combined with individualized nutrition counseling. An explanation for this superiority is not clear but may have to do with the type of fiber within chia seeds and their ability to promote satiety.