What shift workers can do to moderate the adverse effects of circadian rhythm disruption.
The Metabolic Harms of Night Shifts and Irregular Meals
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Below is an approximation of this video’s audio content. To see any graphs, charts, graphics, images, and quotes to which Dr. Greger may be referring, watch the above video.
Shift workers may have higher rates of death from heart disease, stroke, diabetes, dementia, cardiovascular disease, and cancer. Graveyard shift, indeed! But, is it just because they’re eating out of vending machines, or not getting enough sleep? Highly controlled studies have recently attempted to tease out these other factors by putting people on the same diets, with the same sleep, but just at the wrong time of day. Redistributing eating to the nighttime resulted in elevated cholesterol, blood pressure, and inflammation. No wonder shift workers are at higher risk; shifting meals to the night in a simulated night shift protocol turned about a third of the subjects effectively prediabetic in just 10 days. Our bodies just weren’t designed to handle food at night.
Just as avoiding bright light at night can prevent circadian misalignment, so can avoiding night eating. We may have no control over the lighting at our workplace, but we can try to minimize overnight food intake, which has been shown to help limit the negative metabolic consequences of shift work. When we finally do get home in the morning, though, we may disproportionately crave unhealthy foods. In this experiment, 81% of participants in a nightshift scenario chose high-fat foods such as croissants out of a breakfast buffet, compared to just 43% of the same subjects during a control period on a normal schedule.
Shiftwork may also have people too fatigued to exercise, but even at the same physical activity levels, chronodisruption can affect energy expenditure. Researchers found that you burn 12-16% fewer calories while sleeping during the daytime compared to night. Just a single improperly-timed snack can affect how much fat you burn every day. Study subjects eating a specified snack at 10 am burned about 6 grams more fat from their body than on the days they ate the same snack at 11pm. That’s only about a pat and a half of butter’s worth, but it was the identical snack––just given at a different time. The late snack group also suffered about a 9% bump in their LDL cholesterol within just 2 weeks.
Even just sleeping in on the weekends may screw up our metabolism. “Social jet lag” is the discrepancy in sleep timing between our work days and our free days. From a circadian rhythm standpoint, when we go to bed late and sleep in on the weekends, it’s as we flew a few time zones west on Friday evening and fly back Monday morning. Travel-induced jet lag goes away in a few days, but what might the consequences be of constantly shifting your sleep schedule every week over your entire working career? Interventional studies have yet put it to the test, but population studies suggest that those who have at least an hour of social jet lag a week (which may describe more than two-thirds of people) have twice the odds of being overweight.
If sleep regularity is important, what about meal regularity? The importance of regular meals at roughly the same time every day was evidently emphasized by such luminaries as Hippocrates and Florence Nightingale, but wasn’t put to the test until the 21st century. A few population studies had suggested that those eating meals irregularly were at a metabolic disadvantage, but the first interventional studies weren’t published until 2004. Subjects were randomized to eat their regular diets split up into 6 regular eating occasions a day, or 3 to 9 a day in an irregular manner. Researchers found that eating an irregular pattern of meals every day can cause a drop in insulin sensitivity and cause cholesterol levels to rise, and reduce the calorie-burn immediately after meals in both lean and obese individuals. They ended up eating more, though, on the irregular meals. And so, it’s difficult to disentangle the circadian effect. The fact that overweight individuals may overeat on an irregular pattern may be telling in and of itself, but it would be nice to see such a study repeated using identical diets to see if irregularity itself has metabolic effects. And, just such a study was published in 2016.
During two periods, people were randomized to eat identical foods in a regular or irregular meal pattern. During the irregular period, people had impaired glucose tolerance––meaning higher blood sugar responses to the same food, and lower diet-induced thermogenesis––meaning burned fewer calories to process each meal. The difference in thermogenesis only comes out to be about 10 calories per meal, and indeed there was no difference in weight changes over the two-week periods. But diet-induced thermogenesis can act as a satiety signal. The extra work put into processing a meal can help slake one’s appetite. And indeed, lower hunger and higher fullness ratings during the regular meal period could potentially translate into better weight control over the long term.
Please consider volunteering to help out on the site.
- Jiang P, Turek FW. The endogenous circadian clock programs animals to eat at certain times of the 24-hour day: what if we ignore the clock? Physiol Behav. 2018;193(Pt B):211-7.
- Lennernäs M, Akerstedt T, Hambraeus L. Nocturnal eating and serum cholesterol of three-shift workers. Scand J Work Environ Health. 1994;20(6):401-6.
- Morris CJ, Purvis TE, Mistretta J, Hu K, Scheer FAJL. Circadian misalignment increases C-reactive protein and blood pressure in chronic shift workers. J Biol Rhythms. 2017;32(2):154-64.
- Morris CJ, Purvis TE, Hu K, Scheer FA. Circadian misalignment increases cardiovascular disease risk factors in humans. Proc Natl Acad Sci USA. 2016;113(10):E1402-11.
- Scheer FA, Hilton MF, Mantzoros CS, Shea SA. Adverse metabolic and cardiovascular consequences of circadian misalignment. Proc Natl Acad Sci USA. 2009;106(11):4453-8.
- Mattson MP, Allison DB, Fontana L, et al. Meal frequency and timing in health and disease. Proc Natl Acad Sci USA. 2014;111(47):16647-53.
- Grant CL, Coates AM, Dorrian J, et al. Timing of food intake during simulated night shift impacts glucose metabolism: a controlled study. Chronobiol Int. 2017;34(8):1003-13.
- Cain SW, Filtness AJ, Phillips CL, Anderson C. Enhanced preference for high-fat foods following a simulated night shift. Scand J Work Environ Health. 2015;41(3):288-93.
- McHill AW, Melanson EL, Higgins J, et al. Impact of circadian misalignment on energy metabolism during simulated nightshift work. Proc Natl Acad Sci USA. 2014;111(48):17302-7.
- Hibi M, Masumoto A, Naito Y, et al. Nighttime snacking reduces whole body fat oxidation and increases LDL cholesterol in healthy young women. Am J Physiol Regul Integr Comp Physiol. 2013;304(2):R94-101.
- Parsons MJ, Moffitt TE, Gregory AM, et al. Social jetlag, obesity and metabolic disorder: investigation in a cohort study. Int J Obes (Lond). 2015;39(5):842-8.
- Roenneberg T, Allebrandt KV, Merrow M, Vetter C. Social jetlag and obesity. Curr Biol. 2012;22(10):939-43.
- Mota MC, Silva CM, Balieiro LCT, Fahmy WM, Crispim CA. Social jetlag and metabolic control in non-communicable chronic diseases: a study addressing different obesity statuses. Sci Rep. 2017;7(1):6358.
- Pot GK, Almoosawi S, Stephen AM. Meal irregularity and cardiometabolic consequences: results from observational and intervention studies. Proc Nutr Soc. 2016;75(4):475-86.
- Farshchi HR, Taylor MA, MacDonald IA. Regular meal frequency creates more appropriate insulin sensitivity and lipid profiles compared with irregular meal frequency in healthy lean women. Eur J Clin Nutr. 2004;58(7):1071-7.
- Farshchi HR, Taylor MA, MacDonald IA. Decreased thermic effect of food after an irregular compared with a regular meal pattern in healthy lean women. Int J Obes Relat Metab Disord. 2004;28(5):653-60.
- Farshchi HR, Taylor MA, MacDonald IA. Beneficial metabolic effects of regular meal frequency on dietary thermogenesis, insulin sensitivity, and fasting lipid profiles in healthy obese women. Am J Clin Nutr. 2005;81(1):16-24.
- Alhussain MH, MacDonald IA, Taylor MA. Irregular meal-pattern effects on energy expenditure, metabolism, and appetite regulation: a randomized controlled trial in healthy normal-weight women. Am J Clin Nutr. 2016;104(1):21-32.
- Parks EJ, McCrory MA. When to eat and how often? Am J Clin Nutr. 2005;81(1):3-4.
- Jørgensen JT, Karlsen S, Stayner L, Andersen J, Andersen ZJ. Shift work and overall and cause-specific mortality in the Danish nurse cohort. Scand J Work Environ Health. 2017;43(2):117-126.
- Lin X, Chen W, Wei F, Ying M, Wei W, Xie X. Night-shift work increases morbidity of breast cancer and all-cause mortality: a meta-analysis of 16 prospective cohort studies. Sleep Med. 2015;16(11):1381-1387.
- Akerstedt T, Wright KP. Sleep Loss and Fatigue in Shift Work and Shift Work Disorder. Sleep Med Clin. 2009;4(2):257-271.
Image credit: 12019 via pixabay. Image has been modified.
Video production by Glass Entertainment.
Motion graphics by Avocado Video.
Below is an approximation of this video’s audio content. To see any graphs, charts, graphics, images, and quotes to which Dr. Greger may be referring, watch the above video.
Shift workers may have higher rates of death from heart disease, stroke, diabetes, dementia, cardiovascular disease, and cancer. Graveyard shift, indeed! But, is it just because they’re eating out of vending machines, or not getting enough sleep? Highly controlled studies have recently attempted to tease out these other factors by putting people on the same diets, with the same sleep, but just at the wrong time of day. Redistributing eating to the nighttime resulted in elevated cholesterol, blood pressure, and inflammation. No wonder shift workers are at higher risk; shifting meals to the night in a simulated night shift protocol turned about a third of the subjects effectively prediabetic in just 10 days. Our bodies just weren’t designed to handle food at night.
Just as avoiding bright light at night can prevent circadian misalignment, so can avoiding night eating. We may have no control over the lighting at our workplace, but we can try to minimize overnight food intake, which has been shown to help limit the negative metabolic consequences of shift work. When we finally do get home in the morning, though, we may disproportionately crave unhealthy foods. In this experiment, 81% of participants in a nightshift scenario chose high-fat foods such as croissants out of a breakfast buffet, compared to just 43% of the same subjects during a control period on a normal schedule.
Shiftwork may also have people too fatigued to exercise, but even at the same physical activity levels, chronodisruption can affect energy expenditure. Researchers found that you burn 12-16% fewer calories while sleeping during the daytime compared to night. Just a single improperly-timed snack can affect how much fat you burn every day. Study subjects eating a specified snack at 10 am burned about 6 grams more fat from their body than on the days they ate the same snack at 11pm. That’s only about a pat and a half of butter’s worth, but it was the identical snack––just given at a different time. The late snack group also suffered about a 9% bump in their LDL cholesterol within just 2 weeks.
Even just sleeping in on the weekends may screw up our metabolism. “Social jet lag” is the discrepancy in sleep timing between our work days and our free days. From a circadian rhythm standpoint, when we go to bed late and sleep in on the weekends, it’s as we flew a few time zones west on Friday evening and fly back Monday morning. Travel-induced jet lag goes away in a few days, but what might the consequences be of constantly shifting your sleep schedule every week over your entire working career? Interventional studies have yet put it to the test, but population studies suggest that those who have at least an hour of social jet lag a week (which may describe more than two-thirds of people) have twice the odds of being overweight.
If sleep regularity is important, what about meal regularity? The importance of regular meals at roughly the same time every day was evidently emphasized by such luminaries as Hippocrates and Florence Nightingale, but wasn’t put to the test until the 21st century. A few population studies had suggested that those eating meals irregularly were at a metabolic disadvantage, but the first interventional studies weren’t published until 2004. Subjects were randomized to eat their regular diets split up into 6 regular eating occasions a day, or 3 to 9 a day in an irregular manner. Researchers found that eating an irregular pattern of meals every day can cause a drop in insulin sensitivity and cause cholesterol levels to rise, and reduce the calorie-burn immediately after meals in both lean and obese individuals. They ended up eating more, though, on the irregular meals. And so, it’s difficult to disentangle the circadian effect. The fact that overweight individuals may overeat on an irregular pattern may be telling in and of itself, but it would be nice to see such a study repeated using identical diets to see if irregularity itself has metabolic effects. And, just such a study was published in 2016.
During two periods, people were randomized to eat identical foods in a regular or irregular meal pattern. During the irregular period, people had impaired glucose tolerance––meaning higher blood sugar responses to the same food, and lower diet-induced thermogenesis––meaning burned fewer calories to process each meal. The difference in thermogenesis only comes out to be about 10 calories per meal, and indeed there was no difference in weight changes over the two-week periods. But diet-induced thermogenesis can act as a satiety signal. The extra work put into processing a meal can help slake one’s appetite. And indeed, lower hunger and higher fullness ratings during the regular meal period could potentially translate into better weight control over the long term.
Please consider volunteering to help out on the site.
- Jiang P, Turek FW. The endogenous circadian clock programs animals to eat at certain times of the 24-hour day: what if we ignore the clock? Physiol Behav. 2018;193(Pt B):211-7.
- Lennernäs M, Akerstedt T, Hambraeus L. Nocturnal eating and serum cholesterol of three-shift workers. Scand J Work Environ Health. 1994;20(6):401-6.
- Morris CJ, Purvis TE, Mistretta J, Hu K, Scheer FAJL. Circadian misalignment increases C-reactive protein and blood pressure in chronic shift workers. J Biol Rhythms. 2017;32(2):154-64.
- Morris CJ, Purvis TE, Hu K, Scheer FA. Circadian misalignment increases cardiovascular disease risk factors in humans. Proc Natl Acad Sci USA. 2016;113(10):E1402-11.
- Scheer FA, Hilton MF, Mantzoros CS, Shea SA. Adverse metabolic and cardiovascular consequences of circadian misalignment. Proc Natl Acad Sci USA. 2009;106(11):4453-8.
- Mattson MP, Allison DB, Fontana L, et al. Meal frequency and timing in health and disease. Proc Natl Acad Sci USA. 2014;111(47):16647-53.
- Grant CL, Coates AM, Dorrian J, et al. Timing of food intake during simulated night shift impacts glucose metabolism: a controlled study. Chronobiol Int. 2017;34(8):1003-13.
- Cain SW, Filtness AJ, Phillips CL, Anderson C. Enhanced preference for high-fat foods following a simulated night shift. Scand J Work Environ Health. 2015;41(3):288-93.
- McHill AW, Melanson EL, Higgins J, et al. Impact of circadian misalignment on energy metabolism during simulated nightshift work. Proc Natl Acad Sci USA. 2014;111(48):17302-7.
- Hibi M, Masumoto A, Naito Y, et al. Nighttime snacking reduces whole body fat oxidation and increases LDL cholesterol in healthy young women. Am J Physiol Regul Integr Comp Physiol. 2013;304(2):R94-101.
- Parsons MJ, Moffitt TE, Gregory AM, et al. Social jetlag, obesity and metabolic disorder: investigation in a cohort study. Int J Obes (Lond). 2015;39(5):842-8.
- Roenneberg T, Allebrandt KV, Merrow M, Vetter C. Social jetlag and obesity. Curr Biol. 2012;22(10):939-43.
- Mota MC, Silva CM, Balieiro LCT, Fahmy WM, Crispim CA. Social jetlag and metabolic control in non-communicable chronic diseases: a study addressing different obesity statuses. Sci Rep. 2017;7(1):6358.
- Pot GK, Almoosawi S, Stephen AM. Meal irregularity and cardiometabolic consequences: results from observational and intervention studies. Proc Nutr Soc. 2016;75(4):475-86.
- Farshchi HR, Taylor MA, MacDonald IA. Regular meal frequency creates more appropriate insulin sensitivity and lipid profiles compared with irregular meal frequency in healthy lean women. Eur J Clin Nutr. 2004;58(7):1071-7.
- Farshchi HR, Taylor MA, MacDonald IA. Decreased thermic effect of food after an irregular compared with a regular meal pattern in healthy lean women. Int J Obes Relat Metab Disord. 2004;28(5):653-60.
- Farshchi HR, Taylor MA, MacDonald IA. Beneficial metabolic effects of regular meal frequency on dietary thermogenesis, insulin sensitivity, and fasting lipid profiles in healthy obese women. Am J Clin Nutr. 2005;81(1):16-24.
- Alhussain MH, MacDonald IA, Taylor MA. Irregular meal-pattern effects on energy expenditure, metabolism, and appetite regulation: a randomized controlled trial in healthy normal-weight women. Am J Clin Nutr. 2016;104(1):21-32.
- Parks EJ, McCrory MA. When to eat and how often? Am J Clin Nutr. 2005;81(1):3-4.
- Jørgensen JT, Karlsen S, Stayner L, Andersen J, Andersen ZJ. Shift work and overall and cause-specific mortality in the Danish nurse cohort. Scand J Work Environ Health. 2017;43(2):117-126.
- Lin X, Chen W, Wei F, Ying M, Wei W, Xie X. Night-shift work increases morbidity of breast cancer and all-cause mortality: a meta-analysis of 16 prospective cohort studies. Sleep Med. 2015;16(11):1381-1387.
- Akerstedt T, Wright KP. Sleep Loss and Fatigue in Shift Work and Shift Work Disorder. Sleep Med Clin. 2009;4(2):257-271.
Image credit: 12019 via pixabay. Image has been modified.
Video production by Glass Entertainment.
Motion graphics by Avocado Video.
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The Metabolic Harms of Night Shifts and Irregular Meals
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Content URLDoctor's Note
We are winding down this series on chronobiology. Just two videos left in this series: Shedding Light on Shedding Weight and Why People Gain Weight in the Fall.
If you missed any of the earlier ones, see:
- Is Breakfast the Most Important Meal for Weight Loss?
- Is Skipping Breakfast Better for Weight Loss?
- Chronobiology – How Circadian Rhythms Can Control Your Health and Weight
- Eat More Calories in the Morning to Lose Weight
- Breakfast Like a King, Lunch Like a Prince, Dinner Like a Pauper
- Eat More Calories in the Morning Than the Evening
- How Circadian Rhythms Affect Blood Sugar Levels
- How to Sync Your Central Circadian Clock to Your Peripheral Clocks
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