Page 107 - Journal of Special Operations Medicine - Spring 2017

few recent studies have found potentially dramatic im- differences. 21,22 Some persons who engage in low- to
pacts of individual differences in reactions to food types moderate-intensity exercise may notice improvements
and diets. For example, Zeevi et al. found that indi- in physical performance, whereas others may not, and
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viduals varied substantially (and unpredictably) in their some may even see decrements in performance. 17,18,21,22
blood sugar responses to the same foods/meals at differ- In fact, there is speculation that such diets may com-
ent times, despite widely accepted glycemic index values promise high-intensity or anaerobic performance. The
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among the foods. They concluded that universal dietary role of ketogenic diets in cognitive performance is just
recommendations would have limited usefulness given beginning to be investigated, so benefits have not yet
the diverse responses among individuals. By incorporat- been substantiated except in populations with neuro-
ing individual differences to the same foods, researchers logical or neurodegenerative disorders. Overall, it ap-
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demonstrated that tailored dietary approaches were pears that the lack of consistent performance benefits
more successful in achieving weight loss and blood may reflect individual metabolic differences, which need
sugar control compared with generic “healthy” diet rec- to be identified if such diets are to be incorporated into
ommendations. Next, we offer just three examples of a P2 approach.
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how nutritional and supplemental interventions need
to be tailored to the individual. The examples include Although these three examples are of clear practical im-
creatine and β-alanine supplementation and ketogenic portance on their own, they are only a small fraction of
diets. other ongoing or planned efforts to understand how to
best tailor dietary practices to lifestyles, genotypes, and
Creatine supplements are very popular and may con- other sources of individual differences. It is very likely
fer selected advantages; in some cases, supplementation that additional factors may have to be considered as we
has been shown to markedly increase the amount of move on to inform a true P2 paradigm. For example,
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creatine in skeletal muscle with some significant perfor- other well-described individual differences, in part due
mance benefits. However, it is clear that people respond to genetic variations, include differential choline re-
differently to ingestion; there are high, low, and non- quirements, 25,26 wide variation in sodium losses in sweat
responders. 11–14 The exact reason for such variability is during extended exercise, and a need to individualize
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uncertain, but higher responses have been noted in indi- protocols when athletes ingest sodium bicarbonate to
viduals with normally low muscle creatine stores (e.g., buffer against hydrogen ion accumulation —again, to
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vegetarians). 12 name only a few.

The same holds true for supplementation with β-alanine. Individual Biological Differences
Theoretically, increasing skeletal muscle carnosine
through β-alanine supplementation should improve The complexity of individual biological differences is be-
buffering of hydrogen ions and thereby improve anaero- yond the scope of this article, but several key examples
bic performance. However, individual responses to can highlight what a future P2 may have to incorporate.
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β-alanine supplementation vary widely. High respond- These examples focus on sleep, responses to physical
ers may increase muscle carnosine by approximately training and psychological stress, inherent traits, and
55% and low responders many only increase muscle the microbiome. We briefly discuss the influence of ge-
carnosine by approximately 15%. This may be why a netics, which is likely to be of future importance for P2;
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recent review found, on average, no significant benefit however, genetics as a topic is not emphasized.
of β-alanine supplementation for athletic performance,
despite strong mechanistic reasons to believe there could Sleep requirements and chronotypes
be benefits. Thus, the impact of β-alanine, when con- Several studies have found strong, replicable differences
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sumed daily for about 4 weeks, varies widely. in how much sleep any given individual requires, as
well as whether someone’s general circadian type makes
Our last example focuses on high-fat and ketogenic them more of a “lark” than a “night owl.” 29–31 Research
diets, which are becoming increasingly more popular continues to explore the variability among individual
among certain athletes and military members as a possi- differences to explain the often dramatic (and poten-
ble way to enhance performance. 17,18 A ketogenic diet is tially dangerous) discrepancy between how much sleep
typically very high in fat, moderate in protein, and very people report they need compared with what they objec-
low in carbohydrates (<100g). In contrast to the poten- tively need when tested. 32,33 Yet-to-be identified genetic
tial benefits of a ketogenic diet on multiple disease states influences of sleep requirements, as well individual cir-
(e.g., epilepsy, cancer, diabetes, obesity), 19,20 the scientific cadian patterns, seem to explain why some people tend
evidence does not currently support the use of ketogenic to be better at certain things at different times of the
diets to improve performance, especially in many mili- day. If these differences are known, then individual-
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tary populations. This may be due, in part, to individual ized countermeasures to mediate or mitigate anticipated

Precision Performance: What Does It Mean? 83