Food and Nutrition Board, Institute of Medicine.Dietary reference intakes forcalcium, phosphorus, magensium, vitamin D, and fluoride. Washington, DC:National Academy Press, 1997

4. Matkovic V, Jelic T, Wardlaw GM, et al. Timing of peak bone mass in Caucasianfemales and its implication for the prevention of osteoporosis. J Clin Invest1994;93:799

5. Teegarden D, Proulx WR, Martin BR, et al. Peak bone mass in young women.J Bone Min Res 1995;10:711

6. Johnston CC, Miller JZ, Slemenda CW, et al. Calcium supplementation andincreases in bone mineral density in children. N Engl J Med 1992;327:923

7. Lloyd T, Andon MB, Rollings N, et al. Calcium supplementation and bonemineral density in adolescent girls. JAMA 1993;270:841

8. Lee WT, Leung SS, Wang SH, et al. Double-blind, controlled calcium supple-mentation and bone mineral accretion in children accustomed to a low-calciumdiet. Am J Clin Nutr 1994;60:744

9. Bonjour JP, Carrier AL, Ferrari S, et al. Calcium-enriched foods and bone massgrowth in prepubertal girls: a randomized, double-blind, placebo-controlled trial.J Clin Invest 1997;99:1287

10. Chan GM, Hoffman K, McMurry M. Effects of dairy products on bone and bodycomposition in pubertal girls. J Pediatr 1995;126:551

11. Cadogan J, Eastell R, Jones N, Barker ME. Milk intake and bone mineralacquisition in adolescent girls: randomized, controlled intervention trial. BrMed J 1997;315:1255

12. Weaver CM, McCabe GP, Peacock M. Calcium intake and age influence calciumretention in adolescents. In: Burkhardt P, Dawson-Hughes B, Heaney RP, eds.Nutritional aspects of osteoporosis. New York: Springer-Verlg, 1998:3

13. O’Brien KO, Abrams SA, Liang LK, Ellis KJ, Gagel RF. Bone turnover responseto changes in calcium intake is altered in girls and adult women in families withhistories of osteoporosis. J Bone Miner Res 1998;13:491

14. Weaver CM, Proulx WR, Heaney RP. Choices for achieving dietary calciumwithin a vegetarian diet. Am J Clin Nutr 1999;70:543S

15. Bailey DA, McKay HA, Mirwald RL, Crocker PRE, Faulkner RA. A six-yearlongitudinal study of the relationship of physical activity to bone mineral accrualin growing children: the University of Saskatchewan Bone Mineral AccrualStudy. J Bone Min Res 1999;14:1672

16. Weaver CM. Meeting calcium requirements of physically active people. Am JClin Nutr 2000 (in press)

17. Ruiz JC, Mandel C, Garabedia M. Influence of spontaneous calcium intake andphsycal excercise on the vertebral and femoral bone mineral density of childrenand adolescents. J Bone Min Res 1995;10:675

18. Teegarden D, Lyle RM, McCabe GP, et al. Dietary calcium, protein, andphosphorus are related to bone mineral density and content in young women.Am J Clin Nutr 1998;68:749

19. McCarron DA, Reusser ME. Finding consenses in the dietary calcium-bloodpressure debate. J Am Coll Nutr 1999;18:398S

Brain Function, Mind, Mood, Nutrition, andPhysical Exercise

Wildor Hollmann, MD, PhD, and Heiko K. Stru¨der, MD, PhDFrom the Department of Internal Medicine and Cardiology, Institute of Cardiology and

Sports Medicine, German Sport University, Cologne, Germany

INTRODUCTION

At interdiciplinary congresses, astronomers, physicists, biologists,and medical doctors in different areas of expertise agree: thehuman brain represents the most complex and the least well-researched structure in the known universe. It not only follows theusual laws of physics and chemistry but also produces the “self-reflecting mind,” which can be defined as the ability for abstractthought under self-reflection and planning for the future. Thisaspect is a qualitative difference between humans and animals. The“decade of brain research,” as declared by President Bush of theUnited States in 1989–1990, has been an important period in theacquisition of a great deal of new knowledge on the functioning ofthe human brain.

BRAIN, MIND, AND MOOD

For thousands of years, humans have wondered where the mindoriginates and how the flood of thoughts and ideas could beexplained.Mind is usually the opposite ofbodyandsubstance, i.e.,the physical realm. As distinct from thesoul, themind is charac-terized by the intellect and the ability to think (i.e., reason) andincludes consciousness. In this context, the termmind means the

uniform connection of the psychic experiences of a human being.The scientist, independent of the area of expertise, has to beconcerned primarily with the knowledge of structure, physics, andchemistry and their interaction on the basis of physiologic pro-cesses. This knowledge can then be the foundation for the inter-pretation of the human mind.

Roth1 considered the mind to be a physical state, as are elec-tromagnetic waves, mechanics, heat, or energy. The reason is this:Thoughts, ideas, and thus the mind can be visualized in differentways (e.g., positron emission tomography). The mind can beinfluenced and modified physiologically and pharmacologically.Consequently, Roth1 characterizedvoluntary motor functionas akind of motor state that has its origin in a complex interactionbetween the associated cortical areas and subcortical centers. Thisinterpretation also describes states of mind as subjective experi-ences resulting from specific processes in the brain, which thebrain creates. Thus, one could defineI as a sensorimotor systemandmentalitywith respect to one’s own body.Sensorimotor sys-temdescribes the process by which sensory organs provide infor-mation to the brain through differently firing neurons.Mentalitydescribes the means of comparing and combining sensory activi-ties in relation to a particular memory; the brain develops a“meaning” and evaluates it with brain-immanent criteria. Roth1

called this process “constituents of reality, a construct by thebrain.” Accordingly,mind would be a construct on the basis of aneuronal code plus experience plus current environmental influence.

In the mind, reason (ratio) and emotion (emotio) are confrontedwith each other. In contrast to reason, emotions are experiencednot so much in the brain as in specific parts of the body. Happinessand excitement induce a “pounding heart,” and fear causes a“feeling of pressure in the stomach.” From a biological viewpoint,it is well known that the main guiding principle of behavior is thepromotion of the individual and the survival of the species. Sen-

This study was supported by the Bundesinstitut fu¨r Sportwissenschaft(Cologne, Germany), the Krupp von Bohlen- and Halbach Foundation, andthe Oertel Foundation.

Correspondence to: Wildor Hollmann, MD, PhD, Department of InternalMedicine and Cardiology, Institute of Cardiology and Sports Medicine,German Sport University, Carl-Diem-Weg 6, 50933 Cologne, Germany.E-mail: strueder@hrz.dshs-koeln.de

516 Hollmann and Stru¨der Nutrition Volume 16, Numbers 7/8, 2000

sations such as thirst and hunger, but also the urge to urinate anddefecate, serve for the survival of the individual. Compliance withthese urges, e.g., drinking and eating, is “rewarded” by nature withpositive feelings in the so-called reward centers in the brainresponsible for them. In neighboring areas in the brain, libido andsexual intercourse serve to ensure the survival of the species. To acertain extent, it can be said that nature uses tricks to ensure thesurvival of the individual and of the species. In this context, thesensation of pain presents a warning signal. The sensation is basedon the stimulation of complexes of neurons located mainly in thelimbic system of the brain. The limbic system consists of nucleiand nerves that are interlinked in many ways with the hypothala-mus, brainstem, and especially the cortex. The cortex has a par-ticularly well-developed frontal lobe, where nerves from manybrain areas come together and where projections to other regionsare formed. “Decisions” are made in the same bundles of nervesthat are responsible for motor function. Therefore,mind in thesense ofratio, sensation in the sense ofemotio, and muscularmotor function are superbly linked.

SOME BIOCHEMICAL EFFECTS OF PHYSICALEXERCISE ON THE PSYCHE

During cyclic ergometry, there is a significant augmentation of theregional blood supply in the brain when examined in healthysubjects by means of the 133XE bolus injection method andpositron emission tomography.2 This augmentation may be impor-tant for an acceleration of transport of substances that are increas-ingly produced in the neurons during dynamic exercise. Everyonewho exercises has experienced feeling more relaxed and positiveafter physical exertion. Everyday problems seem to be less signif-icant during the first hours after exercise. Several mechanisms maycause these improvements in mood, which have been objectivelyassessed by psychologic questionnaires. One possible mechanismis the decrease of glucose metabolism in neurons during physicalexercise and the possible compensation by metabolism of ketonbodies.3 This could occur with an improvement in mood. In agespast, the teleologic significance of this improvement in moodwould have been to counterbalance the physical pain during along-lasting fight or attack by an opponent and, thus, be able toendure the physical demand for a longer period. Another possiblemechanism for the better mood may be the release of endorphinsunder the conditions mentioned above.4 The high density of opioidreceptors in the limbic system point in this direction. Also, “en-dorphin increments” during exercise could improve mood. A thirdpossibility for the improvement in mood could be augmentedsynthesis of serotonin or dopamine in the brain. A higher amountof serotonin in the limbic system improves the mood, whereas adecrease of serotonin below a critical threshold promotes thedevelopment of depression. The increase in synthesis of serotoninis based on the augmented entrance of tryptophan into the brain.Two regulatory mechanisms are involved. During long-lastingphysical work, Stru¨der et al.5 found an increased change fromalbumin-bound tryptophan to free tryptophan. This observationaugments the probability that free tryptophan can occupy a carrierfor transport over the blood–brain barrier and, therefore, augmentsserotonin synthesis. The second possible cause of the rise of braintryptophan content during endurance exercise is the decline ofbranched-chain amino acids (CBCAA), which are particularlytaken up by muscle and liver cells in case of depleted glycogenstores.6 This decreases the competition for free tryptophan at itscarrier of the blood–brain barrier. Finally, it should be mentionedthat the decrease of plasma insulin concentration during long-lasting physical work is reversed after exercise. One function ofinsulin is to increase the entrance of BCAA into the muscle cells.This also initiates the mechanism at the blood–brain barrier de-scribed above.

Mood can also be influenced by intake of foodstuffs andstimulants. Caffeine induces its stimulating effect by occupyingthe binding sides of the brain-immanent transmitter adenosin,which can block noradrenergic synapsis, for example. The effectdecreases with time due to habituation. Cocoa and chocolatecontain theobromine and phenylethylamine. The latter is similar toamphetamines in its effects. Thus, these substances may alsoinduce, e.g., reactions of the heart (“heart pounding”). Alcoholinduces an increase of endorphins. The production of the biogenicamino-acid derivatives tetrahydrocaroline and tetrahydropapavero-line is simultaneously increased. Depending on the dose, thesesubstances may improve mood, decrease inhibitions, and augmentsexual desire. The findings mentioned above point to an intensiveconnection between functions of the brain, the cardiocirculatorysystem, and the skeletal muscles on a biochemical basis.

MOLECULAR AND BIOLOGICAL FINDINGS

A synapse is an extremely dynamic unit that can change in 1 msand save information simultaneously. These findings were discov-ered on a scientific basis less than two decades ago. Only recentlywas it proved that neurotransmitters and growth factors occurtogether in neurons. In response to stimuli from the environment orfrom the cerebral cortex itself (thoughts), chemical circuits arebuilt, dissolved, and rebuilt again within a single neuroanatomiclinking. The approximately 1015 synapses in the brain make com-munication a key issue. Thus, the biochemistry of communicationand the “symbolic function” are crucial for the understanding ofthe function of the brain and the mind. The expression of specificgenes changes constantly, with the result that different kinds ofgene products are built, which are important for the flow ofinformation in the nervous system, e.g., genes that are responsiblefor the synthesis of neurotransmitters underlie a complex regula-tion by the environment.7

The fact that any single neuron contains several different trans-mitters leads to an immense, combined potential. The structure ofthe synaptic apparatus is also affected by changes in the environ-ment. Specific experiences change the molecular structure of syn-apses.8 Even the morphology and amount can be modified.9 Forexample, the simultaneous electrical activation of different nervefibers in rats leads to a strengthening of synapses in the hippocam-pus. This synaptic strengthening is calledlong-term potentiation.An increase in the number of synapses and changes in the structureof each individual synapse seems to occur with these changes.10

The neurotransmitter glutamate seems to initiate this process byinteracting with specific receptors in neurons of the hippocam-pus.11 Therefore, a neurotransmitter has two functions in this case:they forward stimulating information within milliseconds and pro-mote the growth of synapses; these actions affect the architectureof the entire circuit.

One of the most astonishing processes is the regulation ofneuronal function by the environment on a genetic level. Throughneuronal impulse activity, the environment has influence on thegenome and, therefore, on neuronal structure and function.12 Thisdynamic presents the central mechanism of information process-ing. It is the communication through the activity of transmittersand tropic and growth factors that mediates constant neuronalreorganization.

The electrical neuronal stimulation rate regulates the chemicalnature of the released transmitters. The transmitter peptide neuronsusually secrete their peptides at a higher impulse rate than thosenecessary for the classic transmitter alone. This is the reason aneuron can function at a very low stimulation rate (,2 Hz) as aclassic transmitter-releasing cell and at a very high impulse rateexclusively as a peptide cell. In the case of medium rates, totallydifferent amounts of both substances can be released.13 The im-portance of this finding is that stimuli from the environment maychange the rate pattern of the impulses and thereby indirectly

Nutrition Volume 16, Numbers 7/8, 2000 517Brain Function, Mind, Mood, Nutrition, and Physical Exercise

influence the form of the biochemical message of the neuron andthus the nature of the information.12

Skeletal and muscle activities influence the response of neuronsin the hippocampus. The hippocampus seems to encode the spatialcontext in the outside world in connection with motor activity ofthe organism.14 The interaction between physical activity, stimulifrom the environment, and the plasticity of the brain down to themolecular level does not leave any doubt that the traditionaldifferentiation between trophic factors, growth factors, and trans-mitters is outdated.12 For example, the classic transmitters seroto-nin and acetylcholine influence the growing process of neurons.Insulin and the insulin-like growth factors function like transmit-ters and regulate the development of neurons and the segmentationactivity of neurons. The human mind, in the sense of the sum ofratio and emotio, is able to initiate an abundance of hormonalreactions. In addition, neurotransmitters can modify existing hor-monal reactions in qualitatively and quantitatively goal-orientedgradation.

NETWORK BRAIN, NETWORK HUMAN BEING

Some brain researchers in past decades were convinced that thegenotype was almost the only decisive factor for the wiring (con-sidered as permanent) between the neurons in the brain. This beliefhas been disproven. The human genome consists of approximately3 billion pairs of bases. One of four bases can be docked to eachplace in the genome; as a consequence, each place contains ap-proximately 2 bits of information, resulting in a total informationcapacity of the human genome of 6 billion bits. In the field ofcomputers, 8 bits equals 1 byte. Therefore, the content of infor-mation in the human genotype amounts to 6–8 billion bytes,equaling 750 megabytes.15

A common compact disk contains approximately 680 mega-bytes of information. Thus, the nucleus of each cell of the humanbody contains information that can fit on approximately one com-pact disk. However, the 750 megabytes of information in thegenotype are opposed by the 1.25 billion megabytes required bythe brain just for coding its connections.15 In other words, if thetotal amount of information in human cells were used only forcoding of links, the capacity would be totally insufficient for agenetic determination. The required amount of information is

greater by a factor of 103–108 (or even more) than the totalcapacity at its disposal. Thus, the human brain cannot have per-manent wiring; human beings learn predominantly by experi-ence.15 The “trick of nature” consists of the construction of neu-ronal networks as information-processing systems. Its flexibility isbased on the immense number of simple circuits. Apart from thebiological facts, the function of a neuron lies in the creation ofmathematical products (input3 weight of the synapsis), the sum-mation of these products, and the comparison of this sum with athreshold value. The work of the calculation is distributed over allneurons and takes place simultaneously, which is the reason it iscalled parallel information processing. Like everywhere else innature, with increasing knowledge about the function of the humanbrain, the view of a dynamic rather than a static element hasbecome prominent. Some researchers have even written of a neo-darwinistic principle in the development of the human brain and itsmind.16

There are surprising distributions of responsibilities in theneuronal nets. The human brain consists of only 0.1% neurons thatare directly active in a sensory or motor manner.17 Thus, 99.9% ofthe cortical neurons receive their input from other cortical neuronsand also project their output to other cortical neurons. Therefore,the brain seems to be concerned mainly with itself.

From these findings, it can be concluded that at an early age,children’s brains should be exposed to as many motor and sensorystimuli as possible. Particularly by means of physical activity,additional synapses could be built and, therefore, isolated neuronsand the associated degeneration could be prevented. Theoretically,the increase of neurons and their respective synapses should pro-vide a better basis for the development of intelligence, which,according to our definition, is the ability to analyze, synthesize,remember, and invent. However, the negative implications alsoshould be considered. For example, children who view violenceand horror on television several times a day will neuronally adapt,so that violence will inevitably be given less importance and willbe considered a “normal” part of their everyday lives. The age-related reduction of dendrites and in particular of spines impairshort-term memory. In this respect, the findings mentioned abovemay be encouraging because intensified physical and intellectualdemands may not only oppose this degeneration in a structural andfunctional way but also may, in the case of appropriate motor

FIG. 1. Possible model of the relations between the origin of thoughts, plasticity of the brain due to gene activation, environment, and behavior.23

518 Hollmann and Stru¨der Nutrition Volume 16, Numbers 7/8, 2000

function and the accompanying increase in regional blood flow andrelease of nerve growth factors, rebuild spines.18

HYPOTHESIS FOR THE ORIGIN OF THOUGHTS ANDTHEIR PSYCHOSOMATIC CONSEQUENCES

Chaotic oscillations of different cell associations exist in the ce-rebrum. They are based on energy-supported exchange processesof ions through neuronal membranes, especially of microtubuli. Asignal from one or from several of the five sensory organs and/orfrom the brain itself induces a uniform alignment of the oscilla-tions in special areas in the prefrontal cortex, the origin of thought.According to this idea, a thought would be identical with exchangeof ions. The signal (information) is compared in the hippocampuswith the long-term memory and then transferred back to theprefrontal cortex. The “created thought” induces, over specific cellmodules in combination with specific electrical excitations, therelease of transmitters from their vesicles, which then promotethrough the nucleus an increased production of the neurotransmit-ter enzymes. The increased synthesis of the transmitter is thenreported to the proper genetic apparatus, which results in a geneactivation with augmented RNA synthesis and the appropriatemRNA. The affected neurons show an increase in the number ofribosomes; therefore, an augmentation of the intended proteinsynthesis will occur. The result is an increased amount of trans-mitter molecules and a change in the neurochemical constellation.Depending on the location and form, this change influences theratio (reason) and/oremotio(feeling). In particular,emotiopassesthrough the hippocampus and pituitary to the hormonal systemand induces an acute, environment-related behavior, based onthe hormonal response adapted to the overall constellation (out-side and inside world). This neurophysicochemical product, i.e.,thought, moves to the sensory areas of the brain (including cerebralareas of hormone production) and back to the prefrontal cortex.The last piece has fallen into place.

According to Churchland,19 cognitive activity only occurs inhuman conciousness if it is represented as a vector or sequences ofvectors within a spacious recurrent system. Crick20 assumed, atleast for visual attention, the existence of a coordinated activity ofneurons at 40 Hz in layers 5 and 6. These layers are actuallyconnected with recurrent loops of several systems including thethalamus and other subcortical structures. A similar opinion hasbeen advocated by Damasio21 and by Llinas and Ribary.22 Theimmense abilities of neuronal networks with recurrent systems andthe building of vector concentrations have been demonstratedseveral times in recent years. Figure 1 schematically shows our

hypothesis,23 which is based on the sum of experimental findingsfrom many research groups.

REFERENCES

1. Roth E.Das Gehirn und seine Wirklichkeit. Frankfurt: Suhrkamp, 19942. Herholz K, Buskies W, Rist M, et al. Regional cerebral blood flow in man at rest

and during exercise. J Neurol 1987;234:93. Herzog H, Unger C , Kuwert T, Hollmann W. Physical exercise does not increase

cerebral metabolic rate of glucose utilization. In:Proceedings of the XVIthInternational Symposion on Cerebral Blood Flow and Metabolism, Miami, FL.1992

4. Arentz T, De Meirleir K, Hollmann W. [The role of opioid peptides during cycleergometry]. Dt Z Sportmed 1986;37:210

5. Struder HK, Hollmann W, Platen P, et al. Alterations in plasma free tryptophanand large neutral amino acids do not affect perceived exertion and prolactinduring 90 min of treadmill exercise. Int J Sports Med 1996;17:73

6. Struder HK, Hollmann W, Platen P, et al. Effects of exercise intensity on freetryptophan to branched-chain amino acids ratio and plasma prolactin duringendurance exercise. Can J Appl Physiol 1997;22:280

7. Black IB, Adler JE, Dreyfus CF, et al. Biochemistry of information storage in thenervous system. Science 1987;236:1263

8. Wu K, Black IB. Regulation of synaptic molecular architecture in a rat sympa-thetic ganglion and hippocampus. J Cogn Neurosci 1989;1:194

9. Greenough WT. Structural correlates of information storage in the mammalianbrain: a review and hypothesis. TINS 1984;7:229

10. Lynch G.Synapses, circuits, and the beginnings of memory. Cambridge: MITPress, 1986

11. Nicoll RA. The coupling of neurotransmitter receptors to ion channels in thebrain. Science 1988;241:545

12. Black IB. Information in the brain. Cambridge: MIT Press, 199113. Bartfai T, Iverfeldt K, Brodin E, Ogren SO. Functional consequences of coexist-

ance of classical and peptide neurotransmitters. In: Ho¨kfelt T, Fuxe K, Pernow B,eds.Progress in brain research. New York: Elsevier Science Publishers, 1986

14. Eichenbaum H, Weiner SI, Shapiro M, Cohen NJ. The organization of spatialcoding in the hippocampus: a study of neural ensemble activity. J Neurosci1989;9:2764

15. Spitzer M. History of neural networks. In: Stein D, ed.Neural networks andpsychopathology. Cambridge: Cambridge University Press, 1998

16. Calvin W. The cerebral symphony: seashore reflections on the structure ofconsciousness. New York: Bantam, 1990

17. Nauta W, Feirtag M.Neuroanatomie. Heidelberg: Spektrum der Wissenschaft,1990

18. Eccles JC.Die Evolution des Gehirns—Die Erschaffung des Selbst. Munich:Piper, 1993

19. Churchland PM.The engine of reason, the seat of the soul. Cambridge: MITPress, 1995

20. Crick FHC.The astonishing hypothesis: the scientific search for the soul. NewYork: Charles Scribner’s Sons, 1994

21. Damasio AR.Descartes’ Irrtum. Munich: Deutscher Taschenbuchverlag, 199722. Llinas R, Ribary U. Coherent 40-Hz oscillation characterizes dream state in

humans. Proc Natl Acad Sci USA 1993;90:207823. Hollmann W, Stru¨der HK. [The human brain as agitator and receptor of muscular

work]. Dt Z Sportmed 1998;49(suppl 1):154

Exercise, Appetite Control, and Energy BalanceJohn E. Blundell, PhD, and Neil A. King, PhD

From the BioPsychology Group, School of Psychology, University of Leeds, Leeds, UK

Given the present worldwide epidemic of obesity, it is pertinent toask how effective exercise could be in helping people to lose

weight or to prevent weight gain. There is a widely held belief thatexercise is futile for weight reduction because any energy ex-pended in exercise is automatically compensated for by a corre-sponding increase in energy intake (EI). In other words, exerciseelevates the intensity of hunger and drives food consumption. This“commonsense” view appears to originate in an energy-balancemodel of appetite control, which stipulates that energy expended

Correspondence to: John E. Blundell, PhD, BioPsychology Group, Schoolof Psychology, University of Leeds, Leeds LS2 9JT, UK. E-mail:johneb@psychology.leeds.ac.uk

Nutrition Volume 16, Numbers 7/8, 2000 519Exercise, Appetite Control, Energy Balance