From Biologic Rhythms to Chronomes Relevant for Nutrition
Franz Halberg,1 Erhard Haus, and Germaine Cornélissen
Not Eating Enough, 1995
Pp. 361–372. Washington, D.C.
National Academy Press
Any one physiologic variable is characterized by a spectrum of rhythms that are genetically anchored, socioecologically synchronized (by the cycles of an environmental niche), and influenced by heliogeophysical effects. Influences can be objectively quantified in terms of cross-spectral coherences. Synchronization is studied (e.g., by shifts of meal timing, such as on shift work, and/or the entire daily routine, such as after transmeridian flights) when different chronome components may adjust at differing rates in any one variable. Blood pressure and heart rate, for instance, reveal a slow adjustment of a built-in approximately 7-d rhythmicity in the face of a rather rapid adjustment of the circadian component in the same variables. Shifts in meal timing have different effects upon different physiologic variables and thus alter internal relations among rhythms at different organization levels, as documented for the
MEAL TIMING IN TERMS OF CALORIES AND SEDENTARY LIMITED MOTOR ACTIVITY
It seems possible to better exploit what is being eaten by scheduling meals. Food consumption could be scheduled for a time when it is physiologically (Goetz et al., 1976; Halberg, 1983, 1989; Halberg et al., 1976, Hirsch et al., 1975; Jacobs et al., 1975) and logistically most useful for body weight maintenance. Specifically, as a countermeasure in the face of underconsumption of rations by workers in the field (such as soldiers), at least one meal should be timed by taking into account the studies carried out in Minnesota on meal timing (Goetz et al., 1976), some of them sponsored by the U.S. Army Institute of Environmental Medicine and the U.S. Army Natick Research, Development and Engineering Center (NRDEC) (Hirsch et al., 1975; Jacobs et al., 1975). These investigations, which compare a single daily meal consumed as a breakfast versus one eaten as a dinner, clearly show a relative
gain in body weight at dinner only versus breakfast only (a statement equivalent to that of a relative body weight loss on breakfast only versus dinner only) (Figures 19-4, 19-5, 19-6, and 19-7). Since in these studies physiologic and psychologic performance were investigated, as were metabolic and endocrine variables, a first recommendation is the completion of analyses of these data (Goetz et al., 1976; Halberg, 1983, 1989; Halberg et al., 1976; Hirsch et al., 1975; Jacobs et al., 1975) on the consequences (concerning body weight and other physiologic and psychologic performance) of consuming one single large meal within 1 hour of awakening (breakfast only) or not before 12 hours after awakening (dinner only). A second recommendation is to extend the scope of the paradigm tested earlier concerning a single meal per day, with several scenarios applied to The Meal, Ready-to-Eat (MRE).
Timing the Kinds of Calories
Specifically, if one had the means, one should repeat the single meal per day study with and without exercise while concomitantly varying the proportions of carbohydrate, fat, and protein, both in the absence of snacks and then with the stepwise systematic addition of timed snacks. With more modest resources, the next step should be tests in the field with exercising and nonexercising individuals consuming three MREs as breakfast, lunch, and dinner versus consuming one-half of an MRE for breakfast, the other one-half MRE for lunch, and two MREs for dinner.
Meal and Performance Timing
In view of a circadian rhythm in the response to exercise (Halberg et al., 1988; Levine et al., 1977), any effect of meal timing on performance could be assessed by having the exercising group complete a standardized routine, for example on a bicycle ergometer. The routine could be repeated at 3-h intervals; at awakening; at 3, 6, 9, and 12 hours thereafter; and at betime. This lab has tested on four subjects a more rigorous schedule, namely exercise at 7 a.m., 10 a.m., 1 p.m., 4 p.m., 7 p.m., 10 p.m., and 1 a.m. each day for up to a month. It would be important to concomitantly evaluate mental performance and alertness on the different schedules. Several studies in his lab have shown that body weight loss may not necessarily be accompanied by a decrease in performance.
Meal Timing and the Body's Time Structure (Chronome)
The Minnesota-Natick studies (Goetz et al., 1976; Halberg et al., 1976; Hirsch et al., 1975; Jacobs et al., 1975) have shown that meal timing is a way to shift physiologic rhythms and that it may amplify the expression of the circadian system, as do certain drugs such as acetyl-L-carnitine (Cornélissen et al., 1992; Portela et al., 1993). It would be worthwhile to determine the most favorable configuration of rhythms in order to assure the peak alertness and performance (e.g., of rangers or pilots) during the most critical times of duty, even if these schedules may be associated with some body weight loss, notably in situations where field duties are of limited duration. Note that at least in the experimental laboratory, food restriction (e.g., to 70 percent of what is consumed ad lib) is associated with a prolongation (Nelson and Halberg, 1986a, b), not a shortening, of the lifespan and also with a lower incidence of mammary cancers (Halberg et al., 1986b).
Analysis of Available Data
Current data suggest that a major meal should be eaten upon conclusion of a daily tour of duty; that is, if the duty starts in the morning, the major meal should be in the evening, or vice versa. In other words, scheduling should be by activity time rather than clock hour. This concept should be explained in an appropriate communication to commanding officers, so that it is reinforced by them and they are able to set a good example, which benefits themselves and their troops. In the interim, the wealth of data accumulated in the Minnesota-Natick studies and additional data to be obtained should be used to assess the relationship between performance and body weight change. This
effort would benefit from further experimental studies in the laboratory and in the field. Such retrospective analyses are recommended, and the sooner the better. Endocrine and performance data are available in Minnesota from meal-timing studies that have thus far been the subject only of a technical report (Graeber et al., 1978). Data collected, for example by L. A. Stephenson and M. A. Kolka at NRDEC on the adrenal cycle (Personal communication, 1993), would benefit from a chronobiologic assessment that can provide an individualized assessment of statistical significance.
Prospective Studies on Optimization of Dietary Supplements
Autopsies on very young American soldiers killed in battle during the Korean War revealed some vascular changes and suggested the need for prophylaxis by that age if not earlier (for review, see Halberg et al., 1986a). The methods of chronobiology allow level of risk to be detected by means of chronophysiologic monitoring (instead of relying on time-specified spot checks, biopsies, and autopsies) (Cornélissen et al., 1993; Halberg et al., 1993). Differences in dynamic features of blood pressure variation are found between the offspring of parents with and without high blood pressure and/or other cardiovascular disease (Halberg et al., 1990). Such differences as a function of family history of cardiovascular diseases are found early in life: shortly after birth and in adolescents. An unduly amplified circadian rhythm of blood pressure can be interpreted as presenting a heightened risk for vascular disease, notably stroke and nephropathy (Otsuka, 1994). Thus arises the opportunity for the Army to identify a portion of the population at risk and develop procedures for preventing a further deterioration of the vascular system and preferably for reversing changes that are already in place.
Dietary modification, such as the use of supplements, is one approach toward this goal. Much chronobiologic evidence from cooperative studies reveals the need to time the administration of dietary supplements according to rhythms. It has, for instance, become apparent that the effects of aspirin may be circadian stage-dependent, notably some prophylactic effects that may be related to the antiplatelet activity of aspirin (Cornélissen et al., 1991; Prikryl et al., 1991, 1993). Host tolerance of aspirin is also time-dependent (Siegelova et al., 1993). The best compromise between efficacy and tolerance must therefore be sought for prophylactic uses of aspirin. The same considerations apply to carnitine preparations that have a circadian stage-dependent effect upon blood pressure and heart rate (Cornélissen et al., 1994; Portela et al., 1993). Documenting this putative time-dependence on an appropriate scale and implementing the study of other dietary supplements given to recruits at the beginning of the tour of duty may be within the scope of Army nutrition.
Such a study would gain from including an echocardiogram and a 7-d ambulatory blood pressure and heart rate profile at the outset, with the
measurements repeated 1 year later. The risk indices reflected by the pattern of blood pressure variation could thus be correlated with left ventricular mass and other indices of the heart morphology obtained by echocardiography (Cornélissen et al., 1994; Kumagai et al., 1992). If, in addition, the recruits can be persuaded to keep a precise diary of when and what they eat, it might be possible to study associations between any alteration of the cardiovascular chronomes and patterns in the relative consumptions of carbohydrate, fat, protein, and/or dietary supplements. Further guidelines may thus be derived for making recommendations of what to eat when. Given the age of recruits, this may be the best opportunity to carry out such nutritional studies with an aim toward prevention and self-help according to a chronobiologic approach now being advocated by the American Association for the Advancement of Science in a newly released report (Cornélissen, 1994; Culotta, 1993).
As an aside, the first author was most happy during the post-World War II years in Austria to receive U.S. Army rations in the form of CARE packages. These were—and in the authors' opinion still are—invaluable, the difference in circumstances notwithstanding.
If it is impossible a priori to know how much food will be consumed by military personnel, and if a complete consumption of the ration cannot be realized, it seems reasonable that rations could be packaged so that unused portions can be saved and consumed at a later time or recycled for human and/or other use rather than discarded as waste. This would be a step beyond the technology that makes possible shelf-stable meals that do not require refrigeration before opening, but also a step far beyond our competence.
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