Are you more likely to gain weight if you eat late at night?

Introduction

I was invited on to BBC Radio to give a definitive, evidence-based answer to the above question. In preparation, I took a deep dive into the scientific literature to gather and critically appraise the latest, evidence-based insights. This article summarises my findings. For a quick overview, listen to the interview (just click play below), or read on for the full lowdown.

In short, the answer is a resounding yes! For two reasons. One, because our eating behaviours are different at night. And, two, preliminary evidence suggests that calories also count for more at night, due to the influence of our circadian rhythm (24-hour sleep-wake cycle) on metabolism. Put another way, there is early but very strong evidence that a calorie is not always a calorie – rather, our bodies process calories more sparingly at night. Let’s take each of these factors in turn, looking at behaviour first, where the evidence is cut and dried.

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1) Behaviour

Late eaters tend to eat more

Firstly, those who eat at night tend to eat more (i.e. have higher calorie intakes) than early eaters.[1,2] They are therefore more likely to exceed their energy requirements; over time, any surplus will lead to weight gain. Further analysis reveals that the relationship between late eating and higher calorie intake is mediated by greater eating frequency[2] – late eaters eat more times per day than early eaters – suggesting that their ‘eating window’[i] is prolonged, rather than pushed out into later in the day.

Late eaters often make poorer food choices

Secondly, late eaters often make poorer food choices. At night, you’re more likely to reach for high-calorie foods like pizza, crisps, biscuits, ice cream, for a number of different reasons:

• Convenience – late-night eaters may not have easy access to healthy food. Many studies suggest that night-workers tend to snack on unhealthy foods due to lack of availability of healthy options in the workplace at night[3-5]

• Emotional eating – if you’re an emotional eater, stress,[6] anxiety, boredom[7] or sadness[8] can all increase food intake

• Tiredness – lack of sleep mucks up our appetite-regulating hormones, lowering leptin (appetite-suppressant, known as the ‘satiety hormone’) and raising ghrelin (appetite-stimulant, known as the ‘hunger hormone’), resulting in increased hunger and food intake the next day, especially high-calorie, high-carbohydrate foods[9-12]

• Television watching – not only do people eat more when watching TV,[13,14] they reach for higher calorie foods.[15]

2) Circadian rhythms

Now, let’s turn to the question of timing: does eating late at night have an independent effect on weight? The idea that calories count for more at night has been hotly debated. When I studied nutrition, some 20 years ago, we were taught that weight control was simply a matter of calories in, calories out. It didn’t matter what you ate or when you ate. But more recent evidence indicates that weight control is more complex than that.

The argument that eating at night makes you gain weight originally stems from animal studies, which suggest that the body may use consumed calories differently past a certain time of day. Several studies on mice show that mice that eat during their normal sleeping phase put on more weight than mice that only eat during their ‘daytime’ hours, despite being fed the same number of calories.[16-18]

Obviously, extrapolating from mice to humans is problematic, but evidence from human studies followed. Initially, from those with observational designs, providing consistent if not incontrovertible support. However, last year, results were published from a randomised controlled trial – the gold standard in study design, the strongest kind of scientific evidence that you can get – providing the first experimental evidence that eating late or closer to sleep onset leads to weight gain.[19]

The study, by Goel et al.[19], was small, but very well designed, cleverly using a within-subjects crossover design to observe the effects of eating the same number of calories across a daytime eating schedule (8am-7pm) versus delayed (12pm-11pm). Participants followed each schedule for 8 weeks with a 2-week washout period in between. Sleep and physical activity – potential confounding variables – were held constant. Weight, body composition and various metabolic markers (blood glucose, insulin, cholesterol) all improved on the daytime schedule. We’ll need to see the results of this study replicated before we can draw firm conclusions, but the preliminary evidence suggests that, yes, it is indeed true that if you eat late at night, you're more likely to gain weight (and have a less favourable metabolic profile), independent of the amount of calories you consume or the amount of sleep you get.

Your biological clock hour is more important than clock hour

If you’re now wondering, what’s the cut off point for when you should stop eating, further research indicates that it’s not clock hour that’s most important, but biological clock hour.[20] Specifically, the start of your own biological night, defined as the point of melatonin onset, which occurs about two hours before bedtime/sleep onset. McHill et al. found that non-lean individuals consumed most (more than 50%) of their calories closer to or after melatonin onset (i.e. at a later biological time) than lean individuals; they also stopped eating at a later biological time.[20]

Circadian rhythm varies greatly from person to person, whether due to irregular work shifts or simply natural preference for rising early or staying up late. In the above study, on average, melatonin onset/biological night onset was around 11/11.30pm, but ranged from as early as 9.30pm to just after 1am.[20] To identify the start of your own biological night, simply subtract two hours from when you usually fall asleep and don’t eat after that point. Also, try to front end your calorie consumption, that is, try to eat most of your calories earlier in the day, not too close to onset of your biological night.

Underlying mechanisms

• The thermic effect of food (TEF) decreases from morning to night.[21-23] TEF is the number of calories the body spends making food available to itself – it is the sum of energy expenditure required for the digestion, absorption, metabolism and storage of food. If you eat a meal or snack late at night, it costs the body less to process that food than the same meal or snack eaten earlier in the day. One study quantified the saving at 4%.[21] In controlled laboratory settings using whole-room indirect calorimetry, the TEF response to a meal consumed at around 10.30pm decreased by approximately 4% relative to the same meal at around 6.30pm. I know that 4% doesn’t sound like much, but if you consistently eat later that energy saving would add up, contributing to potential positive energy balance and weight gain over time.

• Our internal circadian clock increases hunger and appetite at night,[24] independent of food intake, which could explain why late eaters tend to eat more.

Sonnda’s 5 steps for success

Follow these five simple strategies to regulate your appetite, avoid late-eating weight gain, and optimise your metabolic health.

1. Make sure you get enough sleep – sleep loss mucks up your hunger hormones and is an independent risk factor for weight gain and metabolic dysfunction. The Sleep Foundation recommends 7-9 hours/night for adults aged 18-64 and 7-8 hours for older adults (aged 65+).[25] Pay attention to sleep quality too; it’s not just duration that counts.
   

2. Avoid eating after onset of your personal biological night, defined as two hours before your usual bedtime/sleep onset.
   

3. Also, try to eat most of your calories earlier in the day, not too close to onset of your biological night.
   

4. If you feel genuinely hungry in the two hours before bed (i.e. after onset of your biological night), eat a small, nutrient-dense snack, around 150 calories[26] (nothing sugary or high in refined carbs as that can affect your blood glucose at night, leading to night-time waking). Some great options include: a handful of nuts; unsweetened, full-fat kefir or yoghurt with a few berries, nuts or seeds; carrot/celery/cucumber sticks with houmous or a spoonful of your favourite nut butter; a bowl of soup; some dinner leftovers. One of my personal faves is a square of 90% dark chocolate dunked into Manilife’s deep roast crunchy peanut butter. Mmmm…
   

5. Regulate your appetite at night and reduce the likelihood of late-night eating by making healthy choices earlier in the day. Opt for balanced meals that comprise all three macronutrients: protein, healthy fats, complex carbs. Pay particular attention to getting breakfast right as studies show that the metabolic benefits can last the whole day, steadying blood sugar levels even after eating lunch[27-30] (known as the ‘second meal effect’[31]) and dinner (daylong effect).[32] Choose low-GI, fibre-rich complex carbs, alongside some protein and healthy fats. E.g. wholegrain or pseudograin porridge with unsweetened, full-fat kefir or yoghurt, berries, nuts/seeds; a vegetable smoothie; eggs, veg and a slice of sourdough bread; oily fish and vegetables. People often don’t think to have veg at breakfast, but once you get over the sweet breakfast stereotype, loads of extra choices open up. At lunch and dinner, have a palm-sized portion of protein (proportional to your needs), cover half your plate with high-fibre, non-starchy veg, add a handful of starchy veg/whole grains/pseudograins/legumes and some healthy fats.

References

1. Gluck ME, Venti CA, Salbe AD, et al. Nighttime eating: commonly observed and related to weight gain in an inpatient food intake study. Am J Clin Nutr. 2008;88(4):900-905. Available from: doi:10.1093/ajcn/88.4.900.

2. Reid KJ, Baron KG, Zee PC. Meal timing influences daily caloric intake in healthy adults. Nutr Res. 2014;34(11):930-935. Available from: doi:10.1016/j.nutres.2014.09.010.

3. Gifkins J, Johnston A, Loudoun R. The impact of shift work on eating patterns and self-care strategies utilised by experienced and inexperienced nurses. Chronobiol Int. 2018;35(6):811-820. Available from: doi:10.1080/07420528.2018.1466790.

4. Reeves SL, Newling‐Ward E, Gissane C. The effect of shift‐work on food intake and eating habits. Nutrition & Food Science. 2004;34(5):216-221. Available from: https://doi.org/10.1108/00346650410560398.

5. Waterhouse J, Buckley P, Edwards B, et al. Measurement of, and some reasons for, differences in eating habits between night and day workers. Chronobiology International. 2003;20(6):1075-1092. Available from: https://doi.org/10.1081/CBI-120025536.

6. Yau YH, Potenza MN. Stress and eating behaviors. Minerva Endocrinol. 2013;38(3):255-267. Available from: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4214609/ [Accessed 23/06/20].

7. Koball AM, Meers MR, Storfer-Isser A, et al. Eating when bored: revision of the emotional eating scale with a focus on boredom. Health Psychol. 2012;31(4):521-524. Available from: doi:10.1037/a0025893.

8. van Strien T, Cebolla A, Etchemendy E, et al. Emotional eating and food intake after sadness and joy. Appetite. 2013;66:20-25. Available from: doi:10.1016/j.appet.2013.02.016.

9. Spiegel K, Tasali E, Penev P, et al. Brief communication: Sleep curtailment in healthy young men is associated with decreased leptin levels, elevated ghrelin levels, and increased hunger and appetite. Ann Intern Med.2004;141(11):846-850. Available from: doi:10.7326/0003-4819-141-11-200412070-00008.

10. Hanlon EC, Van Cauter E. Quantification of sleep behavior and of its impact on the cross-talk between the brain and peripheral metabolism. Proc Natl Acad Sci USA. 2011;108(3):15609-15616. Available from: doi:10.1073/pnas.1101338108.

11. Brondel L, Romer MA, Nougues PM, et al. Acute partial sleep deprivation increases food intake in healthy men. Am J Clin Nutr. 2010;91(6):1550-1559. Available from: doi:10.3945/ajcn.2009.28523.

12. Greer SM, Goldstein AN, Walker MP. The impact of sleep deprivation on food desire in the human brain. Nat Commun. 2013;4:2259. Available from: doi:10.1038/ncomms3259.

13. Chapman CD, Benedict C, Brooks SJ, et al. Lifestyle determinants of the drive to eat: a meta-analysis. Am J Clin Nutr. 2012;96(3):492-497. Available from: doi:10.3945/ajcn.112.039750.

14. Blass EM, Anderson DR, Kirkorian HL, et al. On the road to obesity: Television viewing increases intake of high-density foods. Physiol Behav. 2006;88(4-5):597-604. Available from: doi:10.1016/j.physbeh.2006.05.035.

15. Pearson N, Biddle S. Sedentary Behavior and dietary intake in children, adolescents, and adults: A systematic review. American Journal of Preventive Medicine. 2011;41(2):178-188. Available from: https://doi.org/10.1016/j.amepre.2011.05.002.

16. Arble DM, Bass J, Laposky AD, et al. Circadian timing of food intake contributes to weight gain. Obesity (Silver Spring). 2009;17(11):2100-2102. Available from: doi:10.1038/oby.2009.264.

17. Fonken LK, Workman JL, Walton JC, et al. Light at night increases body mass by shifting the time of food intake. Proc Natl Acad Sci USA. 2010;107(43):18664-18669. Available from: doi:10.1073/pnas.1008734107.

18. Hatori M, Vollmers C, Zarrinpar A, et al. Time-restricted feeding without reducing caloric intake prevents metabolic diseases in mice fed a high-fat diet. Cell Metab. 2012;15(6):848-860. Available from: doi:10.1016/j.cmet.2012.04.019.

19. Goel N, Hopkins C, Ruggieri M, et al. The impact of nighttime eating: A randomized controlled trial of daytime vs. delayed eating on weight and metabolism in adults of normal weight. Sleep. 2019;42(1):A15. Available from: https://doi.org/10.1093/sleep/zsz067.035.

20. McHill AW, Phillips AJK, Czeisler CA, et al. Later circadian timing of food intake is associated with increased body fat. The American Journal of Clinical Nutrition. 2017;106(5):1213–1219. Available from: https://doi.org/10.3945/ajcn.117.161588.

21. McHill AW, Melanson EL, Higgins J, et al. Impact of circadian misalignment on energy metabolism during simulated shiftwork. Proc Natl Acad Sci USA. 2014;111(48):17302-17307. Available from: doi:10.1073/pnas.1412021111.

22. Romon M, Edme JL, Boulenguez C, et al. Circadian variation of diet-induced thermogenesis. Am J Clin Nutr. 1993;57(4):476-480. Available from: doi:10.1093/ajcn/57.4.476.

23. Morris CJ, Garcia JI, Myers S, et al. The human circadian system has a dominating role in causing the morning/evening difference in diet-induced thermogenesis. Obesity (Silver Spring). 2015;23(10):2053-2058. Available from: doi:10.1002/oby.21189.

24. Scheer FA, Morris CJ, Shea SA. The internal circadian clock increases hunger and appetite in the evening independent of food intake and other behaviors. Obesity (Silver Spring). 2013;21(3):421-423. Available from: doi:10.1002/oby.20351.

25. Hirshkowitz M, Whiton K, Albert SM. National Sleep Foundation’s sleep time duration recommendations: methodology and results summary. Sleep Health. 2015;1(1):40-43. Available from: https://doi.org/10.1016/j.sleh.2014.12.010.

26. Kinsey AW, Ormsbee MJ. The health impact of nighttime eating: old and new perspectives. Nutrients.2015;7(4):2648-2662. Available from: doi:10.3390/nu7042648.

27. O'Connor LE, Campbell WW. A novel fiber composite ingredient incorporated into a beverage and bar blunts postprandial serum glucose and insulin responses: a randomized controlled trial. Nutr Res. 2016;36(3):253-261. Available from: doi:10.1016/j.nutres.2015.11.015.

28. Chen MJ, Jovanovic A, Taylor R. Utilizing the second-meal effect in type 2 diabetes: practical use of a soya-yogurt snack. Diabetes Care. 2010;33(12):2552-2554. Available from: doi:10.2337/dc10-0552.

29. Clark CA, Gardiner J, McBurney MI, et al. Effects of breakfast meal composition on second meal metabolic responses in adults with Type 2 diabetes mellitus. Eur J Clin Nutr. 2006;60(9):1122-1129. Available from: doi:10.1038/sj.ejcn.1602427.

30. Jovanovic A, Gerrard J, Taylor R. The second-meal phenomenon in type 2 diabetes. Diabetes Care. 2009;32(7):1199-1201. Available from: doi:10.2337/dc08-2196.

31. Jenkins DJ, Wolever TM, Nineham R, et al. Improved glucose tolerance four hours after taking guar with glucose. Diabetologia. 1980;19(1):21-24. Available from: doi:10.1007/BF00258305.

32. Nilsson AC, Ostman EM, Granfeldt Y, et al. Effect of cereal test breakfasts differing in glycemic index and content of indigestible carbohydrates on daylong glucose tolerance in healthy subjects. Am J Clin Nutr. 2008;87(3):645-654. Available from: doi:10.1093/ajcn/87.3.645.