Review article. Akbar Nikkhah. Abstract. dependent on. postprandial. postprandial. health physiology. Department of *Correspondi

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1 Irnin Journl of Bsic Medicl Sciences Vol. 15, No. 4, Jul-Aug 2012, Received: Jun 16, 2011; Accepted: My 9, Review rticle Eting Time Modultions of Physiology nd Helth: Life Lessons from Humn nd Ruminnt Models Astrct Akr Nikkhh Tissue nutrient supply my e synchronized with endogenous physiologicl rhythms to optimize niml nd humn helth. Glucose tolernce nd insulin sensitivity hve endogenous rhythms tht re not essentilly dependent on food type nd eting. Humn glucose tolernce declines s dy comes into night. Bsed on such evolutionry findings, lrge evening mels must e voided to reduce risks of viscerl diposity, dietes, hypertension nd relted crdiovsculr complexities. Ruminnts s extremely importnt food- reches lrger volume nd fermenttion cpcity. As such, eting time (e.g., evening vs. morning) willl lter producing livestock hve evolved to ruminte mostly overnight when little grzing occurs, nd when rumen postprndil nd diurnl ptterns of food intke, rumen nd peripherl metolites production nd supply, nd milk nd met production efficiency. Most recent discoveries suggest tht eting time modultes postprndil intke nd metolism ptterns in non-grzing lctting cows. Eting rte nd solute intke cn increse y evening vs. morning feeding in diry cows. Evening feeding incresed postprndil rumen voltile ftty cids (VFA) pek, nd surges of lood insulin, lctte nd et-hydroxyutyrte, nd induced periprtl decline in lood glucose. As result, milk ft nd energy production were incresed. While eing unfvorle to humn helth, evening nd night feeding hve proved eneficil to ruminnts. These findings estlish differentil chronologicl sis for food intke nd nutrient metolism in mn nd food- producing nimls. Eting time is mjor externl cue nd fesile life strtegy tht ffects production nd helth physiology. Keywords: Eting time, Helth, Humn, Physiology, Ruminnt Deprtment of Animl Sciences, Fculty of Agriculturl Sciences, University of Znjn, Znjn, Irn *Correspondi ng uthor: Tel: ; Fx: ; emil: nikkhh@znu.c.ir Irn J Bsic Med Sci, Vol. 15, No. 4, July-Aug

2 Akr Nikkhh Introduction Tissue nutrient supply my e synchronized with endogenous physiologicl rhythms to mximize nutrient efficiency nd optimize metolic heth. Such iorhythms re closely linked to eting ptterns (1-3). Postprndil eting ptterns determine dily eting ehvior in ruminnts nd humns (4, 5). Circdin rhythms of cell metolism re shown in endogenous nd exogenous rhythms of lood metolites nd hormones (6, 7). Endogenous rhythms re controlled y the hypothlmic suprchismtic nuclei (Figure 1), nd not only y the environmentl fctors such s photoperiod nd feeding timing (8). Glucose tolernce nd insulin ction re regulted endogenously (9, 10). In contrst, exogenous rhythms re controlled mostly or entirely y externl cues. Blood ure in gots, for instnce, is lrgely responsive to feeding nd digestion nd is, thus, regulted exogenously (7). Feeding time is frm strtegy tht cn lter post-feeding rhythms of ingestion, nutrient ssimiltion, nd peripherl metolite supplies (11-13). Such reflections will indicte optimum times of the 24 hr period when nutrients cn e processed more efficiently for productivity nd helth. A primry ojective of this review rticle is to integrte most recent discoveries on eting time's modultion of humn nd ruminnt physiology. Another ojective is to led such integrtions into development of fesile life strtegies tht cn improve metolism nd helth of humns nd high-producing ruminnts tht re supposed to supply humns with dequtely sfe nd secure food resources. Such conclusive perspectives re essentil for the timely pulic eduction of optimum nutritionl progrms, given the exposure to vriety of environmentl stressors in the new er. Humn physiology models highlights Blood glucose in humns nd rts hs endogenous rhythmicity (9, 10). This mens tht insulin sensitivity nd glucose tolernce vry depending on time of the 24 hr period, regrdless of when eting occurs (10, 14). Glucose tolernce is the reltive mount of glucose tken up y peripherl tissues. Incresed glucose tolernce, which mens higher glucose uptke, results from 1) higher mount of insulin secreted from the pncretic et-cells, 2) incresed glucose trnsporters, nd 3) higher vilility (specificity) nd sensitivity (ffinity) of insulin receptors. Thus, insulin insensitivity is the incresing insulin quntity required to mintin euglycemi. Insulin insensitivity is result of reduced vilility or sensitivity of insulin receptors, which reduces peripherl glucose uptke nd impirs the inhiition of heptic glucose synthesis (9). From n evolutionry viewpoint, humns cnnot metolize glucose s effectively in the evening s they cn in the morning. These re t lest in prt ecuse glucose is demnded most during more ctive times of the dy. Hence, glucose tolernce nd insulin efficiency decline s dy comes into night (15) (Figure 2). Such evolutionry insights re integrted into recommendtion to void lrge evening mels to reduce risks of viscerl diposity, dietes mellitus, nd crdiovsculr disorders. Shift workers should thus e under specil nutritionl regimens to not overet overnight to minimize such risks. Circdin rhythmicity in humn glucose metolism gives rise to lood glucose rhythms tht re not essentilly food-driven (Figures 1-3). This mens tht even during fsting, lood glucose exhiits distinct of the 24 hr ptterns in Figure 1. The suprchismtic nuclei (SCN; iologicl clock) driven rhythms in food intke nd glucose metolism. Blck nd white lines represent night nd dy times, respectively (15). 892 Irn J Bsic Med Sci, Vol. 15, No. 4, July-Aug 2012

3 Eting Time Chronophysiology Figure 2. A model for the suprchismtic nuclei (SCN)-medited regultion of glucose metolism in humn (9, 10) humn lood glucose notwithstnding eting regimen emphsizes the endogenous nture of lood glucose regultion (16). The suprchismtic nuclei regulte lood glucose independent of periprndil food intke ptterns (15) (Figure 3). Meltonin my e involved in food intke nd glucose metolism in humns nd rts (9, 17, 18). For instnce, exogenous meltonin dosed vi drinking wter hs incresed postprndil insulin response (10, 15). Meltonin secretion is siclly induced y drkness. In humns, reduced nocturnl glucose tolernce is concurrent with incresed meltonin secretion (16). Reduced glucose tolernce is due to reduced insulin rection, nd reduced peripherl glucose uptke. These reflect reductions in glucose nd insulin requirements (14, 19), which re iologiclly meningful since glucose should e lest required t times of inctivity or night. The incresed lood glucose could, thus, indicte decline in peripherl glucose uptke nd insulin turnover (17). Insulin nd food ingestion: inter-species intuitions Insulin s the min storge hormone stimultes glucose entry into peripherl dipocytes nd muscle cells (20, 21). Less glucose enters portl vein in ruminnts vs. humns (22). As result, insulin my not hve s significnt effects on heptic glucose uptke nd metolism in ruminnts s it does in humns. Nervous system, gut peptides, pncretic secretions, nd nutrient sorption ll induce insulin relese (23, 24). Nervous-wise, insulin is relesed y the ction of sympthetic nd prsympthetic neurons. Food vision, odor, nd flvor cn lso induce insulin secretion y ctivting prsympthetic neurons in humns. Erlier fundmentl reserch (25-27) Figure 3. Bsl peripherl lood glucose concentrtions (s % of the 24 hr men±sem) cross the light-drk cycle in intct rts (left grph; n=8) nd suprchismtic nuclei (SCN)-lesioned rts (right grph; n=7) under fsting conditions. The lck line res re night times (15) Irn J Bsic Med Sci, Vol. 15, No. 4, July-Aug

4 Akr Nikkhh estlished tht neurl impulses nd gstrointestinl hormones re involved in ruminnt postprndil insulin responses. Secretin nd pncreozymin stimulted insulin relese in sheep (27). The lood insulin rise precedes tht of glucose, suggesting tht glucose is not necessrily mjor cuse of the initil postprndil rise in insulin relese (28, 29). According to the most recent discoveries, such effects depend on eting time. Cows fed once dily t 2100 hr exhiited pre-feeding decline in lood glucose tht progressed until 2 hr post-feeding efore reching the seline t 4 hr post-feeding (12, 13). In 0900 hr-fed cows, however, lood glucose remined constnt without such distinct peri-feeding rhythm (13). As such, postprndil insulin surges were higher for evening vs. morning feeding (30, 31). Thus, insulin ction nd glucose uptke reltions to food provision nd eting depend on when eting occurs. Food presenttion nd milking oth induce eting in individully-fed nd group-housed diry cows (32, 33). Food provisions effects on eting ctivity my well persist even with multiple dily feeding (4). The literture suggests tht diry cows et when fresh food is offered nd tht the mount eten fter food delivery depends on time of dy. Anticiption of food presenttion time my elongte eting time in cows (34). Incresed eting rte shortly fter evening food provision (5, 31) suggests tht cows my nticipte evening feeding etter thn morning feeding. Plsm insulin ws higher nd glucose ws lower t 2 hr post-feeding in evening vs. morning fed cows (30). Higher insulin could weken glucgon, thus reducing gluconeogenesis (20). The intrvenous glucgon hs reduced food intke in sheep (35). It is, therefore, likely tht higher lood insulin nd lower glucose t 2 hr postfeeding in evening fed cows my dely the glucgon-driven stiety nd increse postprndil eting rte (13). In gots fed d liitum for only 3 hr period dily, post-feeding rise in lood insulin occurred (36). This is proly induced y voltile ftty cids (VFA) ffecting the pncretic et-cells. On the other hnd, de Jong (37) oserved post-mel rise in lood insulin of gots without essentilly lood VFA pek. Thus, nervous signls rther thn VFA lone pper directly or vi gut hormones to elicit post-mel insulin response. In lctting cows fed once dily t 0900 hr, lood insulin exhiited distinct diurnl rhythms, with pek t 1745 hr nd ndir during hr (38). A similr lood insulin pek occurred t 1830 hr (39) nd t 1800 hr (40). Thus, diurnl rhythms of peripherl lood insulin re closely relted to eting ptterns. Diurnl ptterns of peripherl lood insulin re more closely relted to food content of non-structurl crohydrtes, such s sugrs nd strch. Ruminnt physiology: evolutionry insights into eting time Evening insted of morning food provision improved eef cttle performnce (41, 42). Lctting cows re extrordinry mmmls with exceptionlly high intke nd production levels ove mintennce (43). Chronoiologicl meditions of rumen nd cow metolism my hence lrgely ffect eting ehvior nd diurnl rhythms of rumen, portl, nd peripherl lood metolites. These will in turn ffect milk iosynthesis nd tissue energy turnover (5, 31). Blood glucose exhiited significnt periprndil responses to food delivery t 2100 hr ut not t 0900 hr (5, 30). Figure 4. Diurnl ptterns of rumintion nd eting in steers grzing lflf pstures (1, 2, 60) 894 Irn J Bsic Med Sci, Vol. 15, No. 4, July-Aug 2012

5 Eting Time Chronophysiology Chronoiologicl meditions of rumen nd intermediry metolism re expected to ffect cow physiology nd milk production. Ruminnts hve evolved to ruminte mostly overnight when little grzing occur nd when the rumen hs een found to hve greter volume thn dy-time (2, 44) (Figure 4). This evolution is consistent with the more nutritious evening vs. morning pstures due to dy-time photosynthesis in plnt leves (45, 46). As such, feeding during night hours, when ruminnts hve evolved to ctively ruminte, ltered postprndil eting ptterns, VFA nd glucose metolism, nd therey peripherl nutrient supply (Figures 5-7). % of dily TMR intke h 3-6 h 1-3 h h h 9-12 h Postfeeding 3-h intervls h h Figure 5. Postprndil food intke ptterns in cows fed t either 0900 hr or 2100 hr. Within ech 3 hr, rs with different superscripts differ t P < 0.05 (1, 2, 5). Plsm BHBA (umol/l) h fed 2100 h-fed 0900 h-fed 2100 h-fed Post feeding hour Figure 6. Postprndil ptterns of plsm lctte nd et-hydroxyutyric cid (BHBA) in cows fed t either 0900 hr or 2100 hr. Within ech smpling time, * = P < 0.05 (1-3, 59) Rumen totl VFA, mmol/l * Post feeding hour Figure 7. Postprndil rhythms of rumen ph nd totl voltile ftty cids (VFA) concentrtions in cows fed t either 0900 hr or 2100 hr. Within ech smpling hour, * = P < 0.05 (2). In humns nd rts, regultion of glucose metolism nd insulin sensitivity depend hevily on time of dy (9, 10, 14). Humns re unle to metolize glucose effectively during evening hours ecuse insulin ction diminishes s dy progresses nd evening egins (15). Accordingly, lrge evening mels must e voided should reducing risks of dietes mellitus nd relted crdiovsculr complexities e imed. It ws only recently tht feeding time effects on postprndil ptterns of intke, rumen fermenttion, nd key lood metolites in lctting cows under thermoneutrl conditions were reveled (Figures 5-7). Diry cows fed t 2100 hr nd 0900 hr ingested respectively 7.6 nd 5.3 kg food within 3 hr of feeding diet with 31.2% neutrl detergent fier (NDF) nd 37.8% non-fier crohydrte (NFC) (31). On less strchy diet, the respective intkes were 11.2 nd 9.0 kg (5). Hence, regrdless of diet composition, evening eting incresed ingestion rte shortly post-feeding. Lctting cows could et s much s 50% of their dily intke only within 3 hr of feeding. Evidently, some individul cows were le to et s much s 70% of their dily intke within only 3 hr of feeding. The greter diet fermentility my reduce intke vi rumen VFA nd mmoni ccumultion (47). As such, the food mount ingested within 3 hr of feeding ws greter with more firous diets. Rumen volume ws greter in cows fed t 2100 hr vs hr (1, 2, 5). The cow s tendency to ingest more food when fed t Irn J Bsic Med Sci, Vol. 15, No. 4, July-Aug

6 Akr Nikkhh 2100 hr vs hr suggests tht the mgnitude of gut-fill effect on intke regultion differs etween morning nd evening. These discoveries re supported y implictions tht food intke is regulted y multitude of diet, niml, nd environmentl fctors (48-50). The greter ppetite following night eting might lso prtly e due to quieter frm environment. Moreover, meltonin regultes glucose metolism (10, 17, 18) nd therey my contriute to food intke regultion. Usully, meltonin is secreted in the sence of light. Evening eting will, thus, coincide with elevted meltonin secretion. In humns, reduced nocturnl glucose tolernce is ssocited with incresed meltonin secretion (16). Assuming reltionship etween meltonin nd glucose metolism in ruminnts lso, diurnl food intke ptterns will depend on when food is presented. Peripherl metolites such s glucose nd VFA depress food intke minly vi cell entries nd not necessrily y stying in the lood (51). Hence, fctors reducing peripherl metolite uptke cn in turn ttenute such metolite-driven stiety. As such, the expected rise in evening lood meltonin might reduce peripherl metolite uptke in insulin-sensitive tissues in fvor of milk iosynthesis. The higher nocturnl meltonin might then weken the food -driven stiety in evening fed cows. This cscde is consistent with the incresed eting rte shortly postfeeding in evening fed cows (2, 5, 31). Such ltered intke regultion might llow possiility for night-time glucose intolernce in lctting cows (30). Milk energy output ws incresed y evening insted of morning eting. This suggests tht t times of greter food intke nd peripherl metolite supply, milk precursors (e.g., lctte, glucose, nd et-hydroxyutyric cid (BHBA)) were tken up more effectively y the mmmry tissue. The higher postprndil rumen VFA nd lood insulin surges y evening vs. morning eting concur with incresed milk energy output in the evening fed cows (Figure 7). In nother study, lctting cows were fed 67% of their diet t 0800 hr nd 33% of it t 1800 hr (52). In ddition, protein supplement ws offered t 15% of dily food intke t either 0830 hr or 0030 hr. Cows te more of the protein mel when it ws offered t 0030 hr vs hr. Consequently, totl food intke ws incresed (16.92 vs kg/d), which led to incresed rumen dry mtter (DM) nd protein digestiility (52). These suggest tht the midnight insted of morning protein mel eting stilized rumen fermenttion. In het stress study, lctting cows were fed 4 times dily different food proportions either during dy s 30% t 0615 hr, 20% t 1000 hr, 25% t 1530 hr, nd 25% t 1900 hr, or during evening s 20% t 0615 hr, 30% t 1530 hr, 25% t 1900 hr, nd 25% t 2100 hr (53). The evening-fed group hd no ccess to food for 5.5 hr during dy. The limited food ccess during dy nd shifting eting time to evening time reduced dily food intke nd energy expenditure. In freezing cold wether, feeding t 2000 hr vs hr improved eef steers growth rte without ffecting food intke (42). In nother eef study (41), heifers fed t either 0900 or 2000 hr in freezing winter were similr in food intke, while evening fed cows hd higher food efficiency. Eting time effects on ruminnt production Midnight insted of morning delivery of protein mel improved milk ft production, most likely y incresed ruminl nutrient digestion (52). No such n effect ws oserved in similr study (54) where lctting cows were fed protein supplement t out 12% of dily intke either t 0830 or 0030 hr. In 118-d lcttion tril, Ahroni et l (53) fed het-stressed lctting cows 4 times during either dy (30% t 0615 hr, 20% t 1000 hr, 25% t 1530 hr, nd 25% t 1900 hr) or evening (20% t 0615 hr, 30% t 1530 hr, 25% t 1900 hr, nd 25% t 2100 hr). Shifting food delivery times from dy into evening improved lcttion persistency nd energy efficiency (53). Others (41, 42) found tht feeding t 2000 hr vs hr improved growth in eef heifers nd steers under freezing winters. Most recently, provision of higher nd lower concentrte diets once dily to lctting cows 896 Irn J Bsic Med Sci, Vol. 15, No. 4, July-Aug 2012

7 Eting Time Chronophysiology t 2100 hr vs hr incresed milk ft nd energy yield (31). The result ws sustntited in following study (2, 11). Energy corrected milk yield ws incresed y 2.1 kg/d in primiprous cows nd y 1.3 kg/d in multiprous cows y evening vs. morning eting. The greter milk ft ws likely due to incresed rumen VFA levels nd higher postprndil peks of peripherl lood lctte nd et-hydroxyutyrte (Figures 6, 7). These were ll linked to incresed eting rte shortly post-feeding in evening vs. morning fed cows (Figure 5). In eef cttle, totl dily intke nd food efficiency hve incresed y evening feeding (55, 56). The science of evolution to optimize rumen nd ruminnt helth Bsed on n evolutionry concept, rumintion occurs mostly overnight (Figure 4). This implies greter rumen digestion cpcity overnight thn during dy. Such greter night-time rumen volume nd fermenttion were recently reveled in grzing (57) nd tiestll housed (1, 2) lctting cows. Should the incresed rumen fermenttion cpcity e concurrent with incresed chewing ctivity nd rumintion, optimum rumen ph nd microil metolism my e more fesile to secure with evening vs. morning feeding. Incresed milk ft y night eting suggests stilized rumen conditions (31). By incresing rumen sorption cpcity, evening eting my not durly lower rumen ph to the rnge in which microil rupture, endotoxins relese, nd proinflmmtory responses occur (e.g.,< ) (58). Endocrinologiclly, insulin stimultes peripherl nutrient uptke. Insulin, however, does not hve mjor impct on propiontedriven heptic gluconeogenesis nd mmmry nutrient uptke (20, 21). Thus, incresed peripherl lood concentrtions of vrious sustrtes y evening vs. morning eting cn increse mmmry nd non-mmmry nutrient flow nd uptke. As result, milk secretion nd peripherl nutrient retention my simultneously improve s shown previously (11, 31). Conclusions nd implictions Metolic chronophysiology is of gret importnce with regrds to eting time effects on the helth of humn nd food-producing livestock. With glucose tolernce declining s dy comes into night, lrge evening mels must e voided to reduce risks of viscerl diposity, dietes, nd consequent crdiovsculr complexities. Such insights hve importnt implictions for shift workers nd those under specil nutritionl regimens. Evening vs. morning feeding of lctting cows under thermoneutrl conditions hs incresed eting rte, therey incresing totl dily intke in given groups of cows. Evening feeding hs lso incresed rumen volume nd postprndil rumen nd peripherl metolite surges. As result, evening feeding hs improved nutrient digestiility nd milk production. Ruminnt evolution to grze minly round sunrise nd sunset nd to ruminte mostly overnight offers perspectives to mnipulte rumen volume, nutrient prtitioning, nd ruminnt helth. Mnipulting eting time cn help to improve production efficiency of food-producing nimls whilst optimizing humn helth. Acknowledgment Environment, The Ministry of Science, Reserch nd Technology, nd University of Znjn, Irn re thnkfully cknowledged for supporting the uthor s progrms of optimizing glol science eduction in the third millennium. References 1. Nikkhh A. Ruminnt chronophysiologicl mngement: n emerging ioscience. Open Access Anim Physiol 2011; 3: Nikkhh A. Eting timing n evolutionry mnger of postmodern rumen physiology nd helth: review. Open Access Anim Physiol 2011; 3: Nikkhh A, Plizier JC, Furedi CJ, Kennedy AD. Kennedy, Response in diurnl vrition of circulting lood metolites to nocturnl vs diurnl provision of fresh feed in lctting cows. J Anim Sci 2006; 84:111. Irn J Bsic Med Sci, Vol. 15, No. 4, July-Aug

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