Danielle DiFranco ’22 and Lauren Park ’22

Introduction

U.S. Olympic Swimmer Michael Phelps told ESPN that he eats between 8,000 and 10,000 calories a day21. This is 4 times the amount of calories an average adult needs. Phelps must have a calorie-dense diet because of the large amount of calories he burns during high levels of physical activity he participates in when training and competing (Zelman, 2008). University of Pittsburgh Director of Sports Nutrition Leslie Bonci, MPH, RD, estimated that, given his 6’4’’ height at 190lb build he would burn about 1,000 calories per hour when training (Zelman, 2008). In comparison, the average adult does not do as much physical activity and therefore does not burn, or need to consume, as many calories. One’s lifestyle and body composition can inform us on what we should eat. 

A more specific term for this concept is personalized nutrition. Personalized nutrition uses a person’s lifestyle and body composition to inform dietary recommendations2. Some factors that influence one’s dietary needs include levels of physical activity, environmental surroundings, and genetics/epigenetics. Epigenetics is different from genetics because it does not refer to changes in the DNA code itself, but rather, the resulting mRNA and proteins. Two fields that inform personalized nutrition are nutrigenomics and nutrigenetics. Nutrigenomics is how nutrients impact genetic/epigenetic mechanisms to influence health, while nutrigenetics is how individual genetic/epigenetic differences affect an individual’s dietary needs13. Together, these topics allow us to study the interactions between the food we eat and our genomes (Figure 1). Here, we investigate potential benefits and controversies regarding the use of personalized nutrition in athletic performance as well as overall health.

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Dietary Supplementation for Athletes

Behind the scenes of incredible athletic performances, like Michael Phelps’ Olympic races, is consistent maintenance of an athlete’s skills and body composition. Dietary supplements, such as antioxidants, have been commonly used as a method of improving athletic ability and exercise performance generally through recovery from oxidative stress. Oxidative stress is when molecules in one’s cell become ‘oxidized’ which means they are toxic to one’s body. However, dietary supplement use has become a controversial topic as studies on their effectiveness reveal harmful effects11. But these studies often fail to take into account individual differences in body composition that could impact the effect of supplementation (Figure 2A)11. Diet and the absorption of nutrients from food varies between people and this changes what nutrients one is deficient in or has enough of. Margaritelis et al. has found that dietary supplements, specifically antioxidants, are only beneficial for exercise if the individual does not already have sufficient levels in their system11. Antioxidants are substances such as vitamins that get rid of the ‘oxidized’ molecules that are toxic to your body. Using antioxidants that one is already sufficient in will have no effect on athletic ability or it could be harmful by hindering the body’s ability to adapt to physical activity11. Think of your body as a cup and an antioxidant as the water in that cup. If your cup is full, i.e. you have enough antioxidants in your body, then when you pour more water into your cup it will overflow. It is not useful to have an overflowing cup, in fact then you have to clean up the mess that the water has made. 

To advance personalized nutrition, Margaritelis et al. suggest that future study designs should take into consideration individual dietary deficiencies when deciding treatment and analyzing study results (Figure 2B)11. In a study by Paschalis et al., when antioxidant supplementation accounted for subject deficiencies, subjects’ athletic performance improved accordingly15. In this study, athletic performance was evaluated by measuring the power produced by the pedaling of a stationary bicycle over 15 mins of cycling15. Creating a personalized nutrition plan to include necessary nutrients and exclude sufficient ones can improve athletic performance.

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Another research team found similar results when studying polyphenols as dietary supplements. Polyphenols are micronutrients that are naturally found in fruits, vegetables, grains, and herbs. They are a type of dietary supplement that is known to be an epigenetic regulator through modulation of proteins18. For example, curcumin is a polyphenol that comes from the spice turmeric18. Curcumin interacts with DNA methyltransferases, microRNAs, and histones acetyltransferases/deacetylases18. These three interactors are epigenetic mechanisms and affect whether or not DNA will be made into proteins. These interactions can help with sports performance because they can decrease inflammation and reduce muscle loss (Figure 3)18. So for example, if you know the activity you are doing will lead to inflammation, you can supplement some curcumin to combat that inflammation. This is an example of personalized nutrition because you are adjusting your diet based on your specific bodily needs. 

The effectiveness of polyphenols as supplements also depends on each individual’s genetic makeup (Figure 3)18. Every person has different mutations in their genome that affect what kind of proteins are made in their cells. These proteins then affect how nutrients are absorbed by one’s body18. The way that polyphenols interact with proteins to change gene expression, and the way genetic mutations change protein expression, both influence how nutrients will be used in one’s body. There is a reciprocal relationship between gene expression and nutrient uptake, which supports the use of a personalized nutrition plan for athletic activity.

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Personalized Nutrition for General Health

We have seen how the food we eat can affect our epigenome in order to achieve better athletic performance. Another use of nutrigenomics studies epigenetic effects of specific nutrients and micronutrients which may affect diet-related diseases. DNA methylation is an epigenetic modification where methyl groups are added to certain DNA bases. Like beads on a necklace, these methyl groups can crowd the DNA strands, making it difficult for the genes to be accessed and transcribed into proteins. A study found that there were significant DNA methylation changes in undernourished youth after supplementation with vitamin B12, but not with folic acid20. These changes were observed in genes whose activities are associated with type 2 diabetes, obesity, insulin function, and glucose and lipid metabolism. Thus, the DNA methylation that results from vitamin B12 supplementation suggests a decreased risk of poor health outcomes like type 2 diabetes and cardiovascular disease for those that are deficient in it. Therefore, it may be possible to personalize vitamin supplementation based on existing individual deficiencies in order to decrease the potential risk of developing diet-related diseases.

Another dietary study looked at the effects of polyunsaturated fatty acids and saturated fatty acids on the epigenome. They found that eating high amounts of saturated fatty acids compared to polyunsaturated fatty acids led to different DNA methylation changes in the fat tissue, specifically in genes that regulate metabolism and inflammation17. They also suggested that a person’s baseline level of DNA methylation might be able to predict weight gain after eating high amounts of fatty acids17. This shows that the components of our diet can have a significant effect on how our body is programmed to metabolize nutrients in the future, and explains why individual people might respond differently to similar diets. 

Nutrigenetics for Food Insensitivities 

In contrast to nutrigenomics, which studies the effect of food on the genome, it is also possible to start from one’s individual genome to inform a person’s food choices. This is known as nutrigenetics, and often begins with taking a DNA test. GenoPalate is one such test that advertises analyzing a person’s genetics and providing them with a personalized nutrition plan7. The GenoPalate claims to “unlock” personalized nutrition needs such as individual micronutrients and macronutrients, sensitivities and substance metabolism, and genetic superfoods7. Studies have been able to validate the use of DNA testing to identify food allergies and sensitivities, since these are often predicted by variations in a single gene, but they are less confident about DNA testing’s ability to predict entire diets or disease risk. 

The benefit of genetic testing is controversial because it is only accurate for certain conditions. Some traits and diseases are highly predictable because they are monogenic, meaning they are caused by variations in a single gene. These include phenylketonuria and galactosemia, as well as lactose intolerance, caffeine sensitivity, and alcohol sensitivity, which were among the most common traits tested by gene testing kits in 20206. Yet, a 2015 study found a lack of association between dietary intake and nutrient-related diseases, such as cardiovascular disease, coronary heart disease, and various gastrointestinal cancers16. The authors looked at 38 genes of interest, and used four different data analysis models, only to find incompatible associations for any of the genes, or weak associations at best. This may be because the likelihood of developing diet-related diseases depends on many different factors in addition to genetics and diet, such as exercise, living and working environment, and socioeconomic status. Therefore, the nutrigenetic approach of using genes to inform diet makes sense if attempting to identify an allergy or sensitivity, but may be less effective at preventing nutrient-related diseases.

Nutrigenetics for the Microbiome

Another way to implement personalized nutrition based on one’s genetics involves the microbiome. The gut microbiome is the collection of bacteria, fungi, and viruses that live in the digestive tract to influence metabolism, and is heavily shaped by genetics8. Some evidence suggests that eating nutrients which are best suited to an individual’s microbiome, or enterotype, might make it easier to achieve health goals like losing weight or improving cardiovascular health. Enterotypes are defined by the specific bacterial species which are most common in the gut: these are Prevotella (P-type), Bacteroides (B-type), or Ruminococcus, though the first two types are the most common4. It was originally thought that these were discrete, fixed characteristics of the microbiome, but newer studies are showing that they overlap (Figure 4)3.

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A way to conceptualize this is that the body is a factory and the bacteria are the workers, and personalizing nutrition means giving the workers the tasks that they are best suited to perform. A study found that individuals with the P-type microbiome who were treated with a high fiber and whole grain diet lost more body fat than those with the B-type microbiome9. So if someone is a “P-type factory,” their bacteria “workers” are more capable of processing plant-based foods like fiber and whole grains to achieve weight loss. These findings show that the metabolic response to food might be individual, depending on the gut microbiome’s composition, suggesting that matching one’s diet to their microbiome might be a new way to personalize nutrition.

Conclusion

Research indicates that personalized nutrition offers a way to both boost athletic performance and improve overall health. Supplementation with polyphenols or vitamin B12 can rewrite the epigenome to increase physical performance and metabolism. Genetic differences can also be analyzed to create personalized diets based on nutrient deficiencies, food sensitivities, or gut microbiome enterotypes. But however exciting these results may be, it is important to remember that the majority of these studies are correlational. Just because researchers have observed that certain diets are followed by certain outcomes does not mean that the diet caused the outcome. There are many factors that contribute to good health besides just diet, as shown in Figure 5. Michael Phelps’s high-calorie diet works for his body not only because of genetics, but also because of his lifestyle and social surroundings. This exemplifies the applications and limitations of personalized nutrition; whether attempting to improve athletic performance, detect a food allergy, or achieve a weight loss goal, personalized nutrition may be considered useful as a cherry on top of an already existing strong foundation of healthy practices.

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References

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