I first came across this fascinating study examining the relationship between seasonal eating and metabolism several months ago and have been vying for time to write a blog post on the topic. I've finally reached the end of my M.S. program in Human Nutrition (I'm graduating this upcoming spring!), so I recently had some time to do a quick write-up on the topic. I think you’ll find this research to be quite interesting and good motivation to focus on eating seasonally!
Eating out of season food alters glucose and fat metabolism
In August of 2018, an article titled “Consumption of cherry out of season changes white adipose tissue gene expression and morphology to phenotype prone to fat accumulation” (whew, that was a mouthful!) was published in the journal Nutrients. (1) The study was conducted on rats fed a “cafeteria diet,” which is a diet used in animal studies filled with high-calorie, palatable foods intended to reflect the processed, unhealthy Standard American Diet. The rats were maintained on a “short-day” schedule, intended to reflect the short day length of winter, and fed cherries, which are out of season in winter. The rats ultimately experienced a handful of adverse metabolic effects in response to this dietary pattern, including the following:
Downregulation of two genes, Bmal 1 and Cry1, that govern circadian rhythms.
Downregulation of Pparα (peroxisome proliferator receptor alpha), a nuclear receptor protein that regulates lipid metabolism in the liver, ketogenesis, and fatty acid β-oxidation. In laymen’s terms, this means Pparα promotes the utilization of fat for energy (aka “fat burning). Animals that lack Pparα are unable to efficiently produce ketones in response to fasting and develop fatty liver.
Decreased expression of Ucp1 (uncoupling protein 1) in white adipose tissue. Ucp1 is protein associated with “browning” (increase mitochondrial production) in adipose tissue, which revs up metabolism. Decreased Ucp1, on the other hand, indicates decreased metabolic function in adipose tissue.
Increased fasting glucose and insulin levels - These changes predispose the rats to insulin resistance and type 2 diabetes.
Decreased expression of genes that promote fatty acid oxidation. Fatty acid oxidation is the process by which the body burns fats for energy.
Increased adipocyte area - Adipocytes (fat cells) grew in response to cherry consumption out of season.
Ultimately, this research suggests that the consumption of cherry out of season adversely affects glucose and lipid homeostasis and promotes fat accumulation when eaten in the context of a Standard American Diet. Eating out of season appears to produce these adverse metabolic effects by disrupting circadian rhythms, the set of biochemical processes within the body that follow an approximately 24-hour schedule and regulate many aspects of our behavior and physiology.
Circadian rhythms are governed by “body clocks,” collections of genes and proteins distributed throughout our tissues that exhibit cyclic activities in response to cues from our environment, such as light/dark exposure, ambient temperature, and timing of food intake. When light, temperature, or food intake cues occur at inappropriate times in a 24-hour cycle, circadian rhythms are disrupted. Exposing your eyes to blue light from electronic devices at night is just one example of a “cue” that disrupts your circadian rhythms.
Circadian rhythm disruption is classically associated with jet lag and disturbed sleep. However, a growing body of evidence indicates that circadian rhythm disruption impacts far more than just our sleep. In fact, it plays a pivotal role in the development and progression of metabolic dysfunctions, including insulin resistance, type 2 diabetes, and obesity. (2, 3) The cherry study in Nutrients builds on this previous research, demonstrating that body clocks in adipose tissue and the metabolic processes governed by those clocks become disrupted when foods at odds with environmental cues, namely changing seasons, are consumed.
Phytochemicals in foods entrain circadian rhythms
How does the body know whether a food is in or out of season? The xenohormesis theory seeks to answer this question. It proposes that phytochemicals in fruits and vegetables have a direct effect on biochemical pathways in animals, including us humans, via evolutionarily conserved signaling pathways. These phytochemicals vary in availability depending on the season. Consuming the phytochemicals available in plants during a specific season helps animals’ biology function optimally during that time period, increasing their chances of survival. Based on this theory, consuming certain fruits and vegetables during the “wrong” season impairs these ancient, phytochemical-controlled signaling pathways in our bodies, ultimately altering our metabolic function.
Eat seasonally for your metabolic health!
While this study was conducted on rats and more research is needed, the available evidence suggests that eating seasonally is important for maintaining optimal metabolic health. Based on these findings, I highly recommend that you make eating seasonally a part of your lifestyle. The best places to find seasonal foods are farmer’s markets and local farms. Eat Wild is a great website that you can use to find organic, biodynamic, and pesticide-free farms in your area offering seasonal, wholesome foods.
Now, I’d love to hear from you! What are your thoughts on this research? Has it motivated you to seek out seasonal foods? Let me know in the comments below.