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Fit Sleep vs. Fasted Sleep!

Fit Sleep vs. Fasted Sleep!

One of the more common practices of people trying to become leaner and more fit is to restrict eating after dinner and going to bed on an “empty stomach”. This sets up a metabolic scenario that is often referred to as fasted sleep, which is supported by couple basic bodily constants. First, during fasted sleep, our metabolism derives more calories from body fat especially as the clock progresses longer through sleep. And second, indulging that late-night sweet tooth close to bedtime would certainly lead to less fat break down and fat burning in general. While these concepts are valid, one big question is whether there is a downside to fasted sleep. Is there something we are overlooking, especially a personal goal involves muscle? In this article, will go deep into fasted sleep and explore some things to consider helping make your dreams come true to lose fat, become leaner, muscular and fit. Its what we like to call fit sleep vs fasted sleep.​

Sleep, Metabolism and Body Fat

Let’s begin by stating that the we don’t have the sleep-fat burning relationship wrong. Sleep is a great time to breakdown and burn body fat as fuel. This is certainly true when the last meal was several hours before you climbed between the sheets. As the absorption of nutrients from your last meal wane, there is a transition to tapping into carbohydrate and fat stores to keep your body going through the night. The liver releases glucose while adipose tissue (body fat) breaks down and releases fat into circulation for use throughout the body. As sleep continues, fat breakdown and burning is optimized, while at the same time metabolism slows down.(1-3) Sleep metabolism is about 0.3-0.45 calories/pound of body weight with fat contributing up to two-thirds. Daily exercise, body composition and level of sleep (e.g. REM) are key influences in addition to the timing and composition of the last meal.

Sleep & Muscle

Whether you are trying to build muscle, enhance sport performance or simply looking to get leaner and more fit, muscle needs to be your first consideration! Muscle, especially trained muscle, will work harder towards your goals than any other body part. More specifically, what happens to muscle if it must regularly endure twelve or more hours between dinner and breakfast? For those trying to make gains in muscle size and strength could this slow our progress? So, be sure look beyond the body fat benefit during sleep, and set your sites on the most important consideration for people who exercise and/or want to be leaner and more fit - the potential impact of fasted sleep on muscle.

It’s now clear that the muscle building processes continue throughout the night.(4-6) So even though you may be off to dreamland, your muscle is still working hard trying to make your performance and fitness goals a reality. A fit body reality that needs to be nourished as efficiently as possible, which includes during sleep to optimize the benefit of your hard work while awake. Meanwhile, for people that struggle to keep weight off; fasted sleep could make weight loss maintenance harder. If calories are restricted through dinner, and protein intake isn’t a priority, fasted sleep will not help protect muscle overnight supporting declines. The loss of muscle and other lean body mass over time lowers metabolism and makes calorie management more difficult over time as well as management of blood glucose and lipids.

Protein & Sleep

Protein in muscle as well as elsewhere in the body is constantly being made and broken down, so that changes over time are the algebraic result of the two. Dietary protein and strenuous exercise, such as resistance exercise or high-intensity interval training can tilt the muscle protein balance scale in favor of building more muscle protein relative to what’s being broken down. Meanwhile, failure to exercise and an inadequate presence of protein in the diet will have the opposite effect, potentially leading to losses of muscle protein over time. Positive changes in muscle, as well as holding on to bigger, stronger, more conditioned muscle, demands on-going exercise and ample protein nourishment from the diet.(7,8)

During sleep, protein is digested, amino acids are absorbed, and muscle proteins are built the same as when you are awake.(6) So rest assured that protein can do its job while you sleep. However, as amino acid absorption from an earlier dinner ends, muscle will slowly transition to a net balanced state and then on to a scenario whereby declining muscle protein building eventually falls below breakdown. So, if you’re trying to build muscle or maintain as much muscle as possible during calorie restriction, then a strategic slug of protein later in the evening makes sense. This is especially true if your protein intake is lagging behind daily requirements which are elevated for people who are exercising for health and fitness or building more muscle or are performance athletes. According to the International Protein Board protein needs are elevated to 1.4 to 1.8 grams/kilogram body weight for people who exercise for better fitness and 1.8 to 2.2 grams/kilogram body weight for performance athletes and those looking to build significant muscle mass and strength.(9)

Nighttime Protein and Body Fat Over the years, many celebrities and trainers have advocated not to eat later in the evening stating that it can negatively impact fat breakdown and burning while you sleep. While this guidance seems logical, it’s important to dig deeper and challenge it, especially as it pertains to protein. First, protein stimulates protein manufacturing in muscle and other tissue which raises metabolism. Second, while proteins can elevate circulating glucose and insulin to a moderate degree at the most, this isn’t the same as similar level of carbohydrate? So what happens when a small, strategic protein-dense supplement or food is consumed before bed? The good news is that researchers have been hard at work to take some of the guesswork out.

For instance, supplemental amounts of protein (e.g. 30 grams whey or casein) taken 30 minutes before bed by young men, were reported to elevate metabolism during the night based on metabolic assessments first thing in the morning.(10) Moreover, casein before bed showed an identical proportion of metabolism coming from fat burning as getting no calories before bed. These results were consistent with similar reports, but this time with overweight women.(11,12) As a bonus, after receiving casein before bed the night before, the women said they were less hungry in the morning.

Looking even closer at indicators of actual fat breakdown during the night, it was reported that consuming a drink containing 25 grams of casein along with 1 gram of leucine 30 minutes before bed, did not disrupt fat breakdown in overweight men as they slept.(13) Here again morning estimates continue to support that casein does not disrupt the coveted a higher percentage of fat burning either. Meanwhile, another study it was reported that a food form of protein (cottage cheese) and protein powder matched calories, protein (grams and type) and leucine content had the same outcome.(14)

Considered together, research studies to date suggest that a strategic, a strategic level of casein and likely other proteins (e.g. 25 to 40 grams) may be consumed at night before bed without a significant impact on fat breakdown and burning during an otherwise unfed state.(15) Meanwhile, the nighttime intake of casein protein would in turn have a positive (anabolic) impact on muscle protein balance during sleep. And, in the grander scheme of daily nutrition, achieving a higher protein intake, which is necessary for building muscle, enhancing performance and/or fitness should include the last protein meal later in the evening, especially if it is necessary to achieve minimum daily protein level.


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  3. Chwalibog A, Thorbek G. Energy expenditure and oxidation of carbohydrate and fat in humans during day and night. Thermochimica Acta. 2002 394(1-2):247-252 ·

  4. Joy JM, Vogel RM, Shane Broughton K, Kudla U, Kerr NY, Davison JM, Wildman REC, DiMarco NM. Daytime and nighttime casein supplements similarly increase muscle size and strength in response to resistance training earlier in the day: a preliminary investigation. J Int Soc Sports Nutr. 2018 May 15;15(1):24.

  5. Snijders T, Res PT, Smeets JS, van Vliet S, van Kranenburg J, Maase K, Kies AK, Verdijk LB, van Loon LJ. Protein Ingestion before Sleep Increases Muscle Mass and Strength Gains during Prolonged Resistance-Type Exercise Training in Healthy Young Men. J Nutr. 2015 Apr 29.

  6. Res PT, Groen B, Pennings B, Beelen M, Wallis GA, Gijsen AP, Senden JM, VAN Loon LJ. Protein ingestion before sleep improves postexercise overnight recovery. Med Sci Sports Exerc. 2012 Aug;44(8):1560-9.

  7. Phillips SM. A brief review of critical processes in exercise-induced muscular hypertrophy. Sports Med (2014): 44 (1): S71-S77.

  8. Phillips SM. Physiologic and molecular bases of muscle hypertrophy and atrophy: impact of resistance exercise on human skeletal muscle (protein and exercise dose effects). Appl Physiol Nutr Metab. 2009 Jun;34(3):403-10.

  9. International Protein Board. Protein Recommendations for Different Populations.

  10. Madzima TA, Panton LB, Fretti SK, Kinsey AW, Ormsbee MJ. Night-time consumption of protein or carbohydrate results in increased morning resting energy expenditure in active college-aged men. Br J Nutr. 2014 Jan 14;111(1):71-7

  11. Kinsey AW, Eddy WR, Madzima TA, Panton LB, Arciero PJ, Kim J, Ormsbee MJ. Influence of night-time protein and carbohydrate intake on appetite and cardiometabolic risk in sedentary overweight and obese women. British Journal of Nutrition (2014), 112, 320–327.

  12. Ormsbee MJ, Kinsey AW, Eddy WR, Madzima TA, Arciero PJ, Figueroa A, Panton LB. The influence of nighttime feeding of carbohydrate or protein combined with exercise training on appetite and cardiometabolic risk in young obese women. Appl Physiol Nutr Metab. 2015 Jan;40(1):37-45.

  13. Kinsey AW, Cappadona SR, Panton LB, Allman BR, Contreras RJ, Hickner RC, Ormsbee MJ. The Effect of Casein Protein Prior to Sleep on Fat Metabolism in Obese Men. Nutrients 2016, 8:452

  14. Leyh SM, Willingham BD, Baur DA, Panton LB, Ormsbee MJ. Pre-sleep protein in casein supplement or whole-food form has no impact on resting energy expenditure or hunger in women. Br J Nutr. 2018 Nov;120(9):988-994.

  15. Kinsey AW, Ormsbee MJ. The health impact of nighttime eating: old and new perspectives. Nutrients. 2015 Apr 9;7(4):2648-62.

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