Have you ever considered what you eat could have a profound effect on how you sleep? It seems funny to pose the question, yet for so many, the thought has not crossed their minds. Recently, Fuelin was sent an update from a current athlete that her consumption of vegetables 45 times over 90 days had been acknowledged by Whoop. The company suggested that this intake of vegetables appeared to be having a positive effect on her REM sleep duration. We thought this was interesting. It deserved a little more attention and explanation. Is Whoop correct in correlating dietary habits to improvements in health metrics and, in particular, sleep? This article will review the role of sleep and diet on health and the effect of diet on sleep duration and quality.
Does sleep and diet impact health?
Let’s review a few pieces of research to understand the interplay between systems and daily habits that can have a large impact on our health. This impact can be both positive and negative in direction. Whilst it would appear obvious that sleep, diet and the two together would have a positive impact, it is not always that clear cut (1). Our diet is commonly recognised as a leading behavioural risk factor for health and disease. By 2030, the United States of America will have close to 1 in 2 adults living with a BMI of >30 (2). This is alarming, yet not limited to the USA alone suffering from a rapid rise in obesity seen worldwide. There is no doubt that nutrition plays a large role in this health crisis, with overconsumption of calories and ultra-processed foods driving the problem to breaking point. Higher consumption of fruit and vegetables is positively associated with reduced mortality and better health outcomes in humans. Simple measures to increase vegetable and fruit intake daily can have a profound impact on body mass, fat mass and overall health.
Improved sleep quality and optimal duration also have a positive impact on human health in terms of risk of diseases such as cancer, cardiovascular disease, diabetes and cognitive decline. (3-5). The mention of optimal sleep duration is important as it is not always the case that more sleep is better. In fact, sleep duration beyond 9 hours daily has been inversely associated with increased mortality. (6) That means too much sleep increases the risk of death. In this particular study, a 33% increase!
The role of sleep and its impact on diet quality is also very interesting. Whilst data is lacking on the causal effect of this, the correlation between either excessively short or excessively long sleep duration indicates that it could also impact general dietary patterns of feeding (7). To date, most research has focused on this direction - the role of sleep impacting dietary choices. Insufficient sleep is associated with increased caloric consumption, poor dietary habits, and obesity; insufficient sleep results in increased snacking and the number of meals consumed daily. The paper's authors also note that increased consumption of food and calories is associated with hedonistic behaviour rather than a physiological requirement to maintain homeostasis. Outlined nicely in Figure 1courtesy of Zuraikat et al, 2021 (1, 8). Sleep quality and duration can also be impacted by many factors. These factors include yet are not limited to the ambient temperature of the room, exposure to bright light before bed, noxious stress, screen time, exercise timing and nutritional intake. A few obvious nutritional candidates that impact sleep include alcohol (read about my personal account on the impact of alcohol on sleep and health metrics here and here), caffeine, water and dairy. Specific macronutrients, proteins (9) and carbohydrates (1) have also been investigated for their role in sleep.
Does nutrition impact sleep?
The obvious question on your lips is, “If sleep (quality + duration) and vegetable/fruit intake affect health, does fruit & vegetable intake affect sleep? The follow-up to this would be, “Is the impact positive or negative?” A recent systematic review investigated the role of diet and its impact on sleep. Their conclusion, based on the available evidence, is that consumption of “healthy foods” mostly refers to the Mediterranean Diet (MedDiet), with high consumption of fruit and vegetables, which was associated with better sleep quality. (10) Adherence to the diet was associated with a reduction in variability in sleep hours per night (<2hrs) along with the improved quality of sleep in several of the prospective studies. Better adherence to the MedDiet was also associated with reduced sleep issues and improved total duration of 6-7 hours per night. An interesting insight is that better adherence to the MedDiet appears to benefit normal and overweight individuals yet not those that are obese. This could relate to other co-existing disease processes, such as obstructive sleep disorders that have a higher frequency in obese populations.
The role of inflammation in the diet has been investigated and put forward as a possible reason for differences in sleep quality. Researchers have used the Dietary Inflammatory Index (DII), a literature-derived score that has been developed to evaluate the inflammatory potential of a diet based on the effect of dietary parameters on inflammatory cytokines. They have found that individuals with higher adherence to a pro-inflammatory diet were more likely to have worse sleep quality. In other words, those that ate a diet high in processed and ultra-processed foods with minimal fruit and vegetables had worse sleep quality. (11)
The reason why diets such as the MedDiet could have a positive impact on sleep is that these types of diets contain foods with higher amounts of tryptophan, serotonin and melatonin. Tryptophan is an essential amino acid found mostly in animal products, such as beef, lamb, pork, poultry, and dairy, as well as in nuts and seeds, whole grains, and legumes. (1) The body produces melatonin via tryptophan in what is called the “Serotonin Pathway”. The process by which melatonin is produced in the body is fairly inefficient, with the vast majority of tryptophan lost to another pathway and also through competition from other amino acids. One proposed method of maximising the availability of tryptophan and improving the efficiency of that pathway is by combining carbohydrates with tryptophan-containing foods. This is because an insulin response transports the other amino acids away to muscle for protein synthesis and thus reduces competition and improves the ability of tryptophan to cross over the blood-brain barrier and be available, firstly for serotonin production and then subsequent melatonin conversion. (12). These steps also require B5 and B6 vitamins plus magnesium, respectively. This is outlined nicely in figure 2 courtesy of Zuraikat et al., 2021 (1).
The bigger picture.
The bidirectional nature of the relationship between sleep and diet is acknowledged however, the research investigating the impact of diet on sleep is lacking compared to that of sleep and its impact on diet. That being said, a growing body of evidence highlights the role of nutrition in influencing sleep quality and duration. More importantly, the quality of nutrition plays an important role in having a positive effect on health and, specifically, sleep. Inflammation in the body is linked to poor sleep quality, increased sleep quantity (hours >9), cognitive issues and other chronic diseases, including heart disease, metabolic syndrome and cancer. These inflammatory markers are often seen with highly processed food consumption combined with a lack of daily vegetables, fruits and grains. Conversely, a diet with high consumption of vegetables, fruits, grains, legumes and dairy results in reduced circulating pro-inflammatory markers such as IL-6 and c-reactive protein (CRP). (13) The exact amount of fruits and vegetables to be consumed per day is still conjecture and theoretical. From a microbiota standpoint, research indicates at least 5 serves of vegetables and fermented foods totalling upwards of 40g+ fibre/day has a positive effect on gut population species and function (14) Consuming between 5 to 7 serves of fruits and vegetables has been shown to reduce the likelihood of short and long sleep occurring. Whilst consumption rate of between 3 to 7 serves per day resulted in a reduced likelihood of poor sleep quality (15). Something else to consider is the previously mentioned notion of consuming carbohydrates with tryptophan-containing foods to improve the production of serotonin and subsequent melatonin. Higher glycemic forms of carbohydrates will maximise the insulin response and thus help this process in the short term yet chronic consumption of high glycemic foods is also known to impact systemic inflammation and increase the risk of disease negatively. It really is a balancing act, context-specific and not a case of black & white when it comes to utilising nutritional strategies to influence health.
Lack of evidence is not always evidence of lack of effect. The studies investigating nutrition and its effect on sleep are still in their infancy. In saying that, common sense should be applied to what we see as a society. A diet consisting of processed, ultra-processed, high-caloric density foods results in negative consequences on health. The impact that this type of diet has on sleep as an aspect of that individual’s health also appears to be negative. With so much focus on sleep at present and the tracking of metrics related to sleep, it is interesting that so little attention is being focused on what we are eating. The focus is so often on the mind from a stress perspective. A constant and consistent reinforcement message by apps and social media to be mindful and meditate more. Perhaps a shift is required? Be mindful, yes. Be mindful of what goes on your plate and into your mouth.
Why not be aggressive and impactful by challenging yourself to increase your intake of vegetables and fruits to a minimum of 5-7 serves per day? This simple act could give you the optimal 7-9 hours of sleep per night. It might just be the change that shifts your sleep data for the better!
Thank you fo reading,
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