Outside the norm but integral in digestion and metabolism
When someone mentions personalised nutrition, there are a number of interpretations that can apply to what that actually means. Traditionally, it meant tailoring food options around an individual’s lifestyle and means, i.e. what foods allow them to get the recommended intake in the most convenient way possible for their circumstances. In standard dietetic practice, personalisation of a meal plan will be created through altering food choices based on chronic disease, nutrient deficiencies, digestive symptoms, intolerances, cooking skills and availability. More recently, personalised nutrition is being related to more factors associated with nutrigenomics and the gut microbiome, with personalised prescriptions being made available from commercial laboratories or through trained health professionals. Solutions to these issues have included specific food selection and supplement intake to target specific nutrients with specific effects.
While this is an excellent start for personalised nutrition, it is very important to understand that there is more to defining metabolic individuality than through genetics and microbiome alone. The phenotype of the digestive system and how it responds to various stimuli like food temperature, food preparation method and timing of food intake all differ based on the individual, and have an impact on the nutrients eventually absorbed and distributed throughout the individual’s body.
Firstly, the anatomy of an individual’s digestive system can vary widely, one of the more commonly reported differences is in the length of the digestive tract. Of interest, the length of the small bowel alone can range from 38-105cm1,2. Physically, a longer bowel length has been positively associated with age3, height4, overall body size3, and gender1. These anatomical differences are also associated with functional and metabolic differences: a longer bowel has been correlated with less frequent defecation, greater risk and incidence of Type 2 Diabetes (diagnosis and HbA1c)2,5, and a higher likelihood of non-alcoholic fatty liver.6. In brief, it is indicated that a longer small bowel may relate to a higher risk of conditions within the metabolic syndrome cluster. While bowel length measurement is more difficult outside of research or surgical settings, it nonetheless reinforces the idea that those individuals with longer small bowel length may benefit from diet therapy that aims to prevent these conditions, i.e. plant based diets.7,8
Secondly, food timing has been shown to have a dramatic influence on the metabolic effect of the food consumed. Of late, some fascinating trials have explored individuals consuming the exact same amount of food, calories and protein/fat/carb breakdown, but experiencing widely varying results due to when the food was eaten. These studies have shown that for individuals at risk of metabolic syndrome (pre-diabetes, T2DM9), or other conditions associated with insulin resistance (polycystic ovarian syndrome10), experience greater improvement in weight, waist circumference, visceral fat deposition and insulin resistance by having fewer meals (2-3 meals vs 6 meals)11, and importantly tapering food intake down through the day, such that dinner occupies a much smaller share (e.g. <20% of the overall caloric intake)12. This fascinating area of study has opened up very exciting insights that align with our already detailed understanding of diurnal variation and the circadian rhythms. The work speaks to the importance and delicate nature of our daily rhythms and their influence on metabolic function in response to food. In conjunction with the established literature around weight loss and food intake to regress these metabolic conditions, appropriate ‘chrononutrition’ may hold the key to create much more consistent results for individuals presenting with them.
Thirdly, food temperature and preparation has been reported to have an influence on an individuals gastro-intesitnal function. Studies are now showing that ingesting colder foods/smoothies can have positive effects on sports performance where a significant increase in body temperature is elicited. Studies have shown that ingestion of a cold drink/smoothie allows prolongation of exercise in a hot environment.13,14. In addition, water at 0.5 degrees and even 19 degrees mitigate the rise in body temp associated with moderate intensity activity.15
In contrast, studies in individuals with functional dyspepsia and gastroparesis have shown that ingestion of cold liquids and food can impair various functions of the gastric system, and influence digestion as a result.16,17. Some of the changes shown after the consumption of colder items include poorer gastric accommodation and gastric perfusion. These effects may be exacerbated with increasing age as thermoregulation is diminished due to loss of fat stores and metabolic rate. While it is recognised that the body is able to heat the food and liquid up to body temperature, there is a period of time where this process is both energy costing and physiologically influential on digestion. How a person responds to food temperature may be a subtle yet important factor to consider when supporting individuals with a more sensitive gastro-intenstinal tract, or those with a lower capacity to thermoregulate.
Overall, personalised nutrition is more than just assessing an individual’s goals, or even knowing their nutrigenomic/gut microbiome profile. Considerations of their physical structure, food timing and even food temperature may be considerations of a greater picture aiming to maximise nutrient absorption and metabolic function for an individual.
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16. Error – Cookies Turned Off. https://onlinelibrary.wiley.com/doi/10.1111/nmo.13491.
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