Timing of food intake is more potent than habitual voluntary exercise to prevent diet-induced obesity in mice

Inappropriate eating habits such as skipping breakfast and eating late at night are associated with risk for abnormal weight-gain and adiposity. We previously reported that time-imposed feeding during the daytime (inactive phase) induces obesity and metabolic disorders accompanied by physical inactivity in mice. The present study compares metabolic changes induced in mice by time-imposed feeding under voluntary wheel-running (RW) and sedentary (SED) conditions to determine the effects of voluntary wheel-running activity on obesity induced in mice by feeding at inappropriate times. Mice were individually housed in cages with or without running-wheels. We compared food consumption, core body temperature, hormonal and metabolic variables in the blood, lipid accumulation in the liver, circadian expression of clock and metabolic genes in peripheral tissues, and gains in body weight between mice allowed access to food only during the sleep phase (daytime feeding; DF) or only during the active phase (nighttime feeding; NF) under SED or RW conditions. Only a high-fat high-sucrose diet was available to the mice throughout restricted feeding. Nocturnal activity was maintained in both NF and DF mice under RW conditions, but significantly suppressed during the latter half of the dark phase in DF mice. Nocturnal fluctuations in core body temperature were maintained in DF and NF mice under both SED and RW conditions, although DF attenuated the day–night amplitude more under SED, than RW conditions. The degrees of DF-induced increases in body weight gain, food efficiency, adipose tissue mass, lipogenic gene expression in metabolic tissues, and hepatic lipid accumulation were essentially identical between SED and RW conditions. Daytime feeding also induced hyperinsulinemia and hyperleptinemia under both SED and RW conditions, although DF-induced hyperleptinemia was slightly attenuated by wheel-running. The temporal expression of circadian clock genes became synchronized to feeding cycles in the liver but not in the skeletal muscle of mice under both SED and RW conditions. Chronic voluntary exercise on running-wheels minimally affected obesity and adiposity in mice caused by daily feeding at unusual times. The timing of food intake might be more important than physical exercise for preventing metabolic disorders. <b>Abbreviations:</b> ANOVA: analysis of variance; DF: daytime feeding; FFA: free fatty acid; GLP-1: glucagon-like peptide-1; HOMA-IR: homeostasis model assessment of insulin resistance; NEAT: non-exercise activity thermogenesis; NF: nighttime feeding; RF: restricted feeding; RW: running-wheel; SCN: suprachiasmatic nucleus; SE: standard error of the mean; SED: sedentary; SPA: spontaneous physical activity; T-Cho: total cholesterol; TG: triglyceride; WAT: white adipose tissues

不吃早餐、深夜进食等不当饮食习惯，与体重异常增长及体脂异常（adiposity）的发病风险密切相关。本团队此前已报道，在小鼠的静息时段（白天）实施限时进食，可诱导其出现肥胖及伴随活动不足的代谢紊乱。本研究通过对比自愿转轮运动（running-wheel, RW）与静息（sedentary, SED）两种条件下，限时进食诱导小鼠产生的代谢变化，以明确自愿转轮运动对不当时段进食诱导的小鼠肥胖的干预效果。

实验小鼠单笼饲养于配有或未配有转轮的笼具中。本研究对比了静息（SED）或自愿转轮运动（RW）条件下，仅在睡眠时段（白天进食，daytime feeding, DF）或活动时段（夜间进食，nighttime feeding, NF）进食的小鼠的多项指标：包括食物摄入量、核心体温、血液激素与代谢指标、肝脏脂质蓄积情况、外周组织时钟基因与代谢基因的昼夜表达模式，以及体重增长情况。整个限时进食（restricted feeding, RF）阶段，小鼠仅可食用高脂高蔗糖饲料。

在自愿转轮运动条件下，夜间进食（NF）与白天进食（DF）小鼠均维持了夜间活动节律，但DF组小鼠的活动在暗周期后半段显著受到抑制。静息与自愿转轮运动两种条件下，DF与NF组小鼠均维持了核心体温的昼夜波动节律；不过相较于RW条件，静息条件下DF组小鼠的体温昼夜振幅衰减更为显著。

在静息与RW条件下，DF诱导的体重增长、食物利用率、白色脂肪组织（white adipose tissues, WAT）重量、代谢组织脂肪合成基因表达，以及肝脏脂质蓄积的升高程度均基本一致。静息与RW条件下，白天进食均会诱导小鼠出现高胰岛素血症与高瘦素血症；不过转轮运动可轻度缓解DF组小鼠的高瘦素血症。

静息与RW两种条件下，小鼠肝脏的生物钟基因的时序表达均同步于进食周期，但骨骼肌中的生物钟基因并未出现此种同步现象。长期自愿转轮运动对非常规时段进食诱导的小鼠肥胖与体脂异常的影响极小。就预防代谢紊乱而言，进食时段可能比体育运动更为关键。

**缩写说明：**
ANOVA：方差分析（analysis of variance）
DF：白天进食（daytime feeding）
FFA：游离脂肪酸（free fatty acid）
GLP-1：胰高血糖素样肽-1（glucagon-like peptide-1）
HOMA-IR：胰岛素抵抗稳态模型评估（homeostasis model assessment of insulin resistance）
NEAT：非运动活动产热（non-exercise activity thermogenesis）
NF：夜间进食（nighttime feeding）
RF：限时进食（restricted feeding）
RW：转轮运动（running-wheel）
SCN：视交叉上核（suprachiasmatic nucleus）
SE：均值标准误（standard error of the mean）
SED：静息组（sedentary）
SPA：自发体力活动（spontaneous physical activity）
T-Cho：总胆固醇（total cholesterol）
TG：甘油三酯（triglyceride）
WAT：白色脂肪组织（white adipose tissues）