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Effects Of Fasting & Time Restricted Eating On Fat Loss & Health

Key Takeaways

  • Sleep-related fasting is particularly important for repair functions in the gut, brain, liver – and can be optimized by not eating 2-3 hours before bed

  • Tenants of ideal time-restricted feeding: (1) delay the first meal at least one hour after waking; (2) don’t eat within 2-3 hours of bedtime; (3) stick to a consistent schedule every day

  • The best target feeding window is 8 hours; shorter windows between 4-6 hours tend to lead to overeating

  • Consistency is best: a feeding window you can stick to in the context of social and life balance is best – if you’re new, try a 12pm-8pm window where no calories are consumed before 12pm and after 8pm

  • From a pure health objective standpoint, it would be best to keep feeding to the middle of the day, i.e., 10am-6pm but this is difficult to sustain socially

  • One meal per day eating seems to lend itself to weight loss but is less likely to be sustained over time

  • To enhance muscle growth, consume protein early in the day – ideally by 10am (which can be difficult considering 8-hour target window)

  • If you’re feeling weak during fast, some salt in water can have a stabilizing effect on blood glucose and give you a boost

What Is Time-Restricted Eating?

  • Time-restricted eating or intermittent fasting means restricting one’s eating to a specific period during a 24-hours day – or going without food for a fixed number of days

  • There is a biological difference between fasting and time-restricted feeding

  • Because we don’t eat during sleep, everyone deploys some sort of time-restricted eating or fasting

  • Time-restricted eating have a powerful impact from weight loss and fat loss to longevity

  • When you eat is just as important as what you eat – it’s important that the feeding window take place during the most active parts of the day

  • The 8-hour feeding window was really born out of time constraints of the lab, not necessarily because it’s the holy grail of feeding times (though it has been repeatedly tested and is a good rule of thumb)

  • Resources for time-restricted eating: myCircadianClock, Zero app

  • Read more: Comprehensive Review On Fasting In Humans

Blood Glucose & Feeding

  • Blood glucose and insulin go up when you eat and down when you don’t eat (barring type 1 or 2 diabetes)

  • What you eat has a differential impact on the rise in blood glucose (e.g., simple carbs and sugars will raise it the most, grains will raise it more than fibrous carbs like lettuce, etc.)

  • High blood glucose is correlated with mortality

  • Almost everyone has an increasing, resting blood glucose level as we age

Effects Of Time Restricted Eating On Hormones

  • In endurance athletes, time-restricted eating led to a significant decrease in free testosterone (not to the extent that it should be avoided unless you have low testosterone at baseline)

  • Studies in athletes have shown significant reductions in cortisol as a result of time-restricted eating

  • Shortening the feeding window to less than 8-hours can increase stress hormones and pro-inflammatory hormones and decrease some sex hormones

  • Effects on fertility: reducing food intake or food calories too much can have negative effects on the ovulation cycle in women and sperm count in men because signals in the brain are looking for good reproductive conditions without stress

  • Alternate day fasting (eating one day, fasting the other) can lead to weight loss and have positive effects on glucose control – but it’s less likely to sustain over time

  • Using time-restricted eating + caloric restriction creates the best hormonal environment for fat loss

Benefits Of Time Restricted Eating

  • If the main goal is to lose weight (i.e., weight loss not health), it doesn’t matter what you eat as long as the calories burned exceed the calories consumed

  • Many factors impact calories burned (e.g., resting metabolic rate, hormones, exercise, non-exercise activity thermogenesis, etc.)

  • Time-restricted eating anchors gene systems of the body and provides a more stable circadian rhythm

  • Benefits you can’t see: regulation of liver health, inflammation, decreased blood pressure, reduced oxidative stress, enhance healthy microbiota, clarity of mind

  • Fasting that takes place during sleep is critical for longevity: during sleep we’re undergoing cellular processes related to reducing inflammation, clearing out debris from the brain that clear dementia

Pillars Of Feeding Protocol

  • 1. Don’t ingest any food first hour after waking up

  • Extend natural deep fast (from sleep) into the morning as long as possible

  • 2. Don’t ingest any calories 2-3 hours before bed

  • Take advantage of a deep fast during sleep: if you eat late in the night, you will not enter fasting for several hours into sleep because your body is still digesting

  • Schedule to maximizes health & social eating: consume calories from 12pm-8pm (meaning no calories after 8pm)

  • Caveat: large meals will take longer to digest than smaller meals

  • 3. Tip: if you want to have an 8-hour feeding window, you should probably think about it as a 6 or 7-hour window because people tend to eat a little past feeding window

  • When people restrict the feeding window too much (i.e., 4-6 hour window), they tend to eat more than metabolic need demands

  • One meal per day: people tend to maintain or lose weight (but there are very few studies on this)

Conditions Of Various Feeding Windows

  • Muscle tissue is better able to undergo protein synthesis early in the day – before 10am ideally which can be tricky to balance when considering 8-hour window

  • If your main interest is in building or maintaining muscle, it’s good to consume protein early in the day regardless of when exercise takes place

  • To start intermittent fasting or shift eating window: allow yourself a transition period of 7-10 days where you shift window one hour until you get to the desired schedule

  • Drifts in the feeding window (e.g., weekends versus weekdays, special occasions) can cause disruptions in circadian clock rhythms that can take several days to recover from

  • Consumption that will not breakfasted state: water, tea (no sugar or milk), coffee (black; data is mixed on plant-based sweeteners)

  • The best way to know what’s going on during feeding and fasting is to wear a continuous glucose monitor (though understandably it’s not desirable for everyone)

Stimulating Transition From Fed State Versus Fasted State

  • Time-restricted eating is really more about accessing fasted state than it is about eating states Glucose clearing through light movement (i.e., 20-minute walk) or light exercise

  • High-intensity interval training later in the day (afternoon) can lower blood glucose and help transition to a fasted state

  • Berberine is over the counter and has effects almost identical to metformin which can mimic fasting; it can be used when consuming high carbohydrate meals but is a little difficult to titrate

  • Feeding and fasting is about setting conditions in the body: you are either promoting cellular growth or cellular repair


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