Time-Restricted Feeding and Its Effects on Obesity, Muscle Mass & Heart Health


Dr. Satchin Panda is a professor at the Salk Institute for biological studies

Where he researches the circadian clock

What is the circadian clock and why it’s so important?

  • It is based on the changing environment of light during a day.
  • It’s particularly important for diurnal animals:
    • Dictates when to go to sleep and wake up.
    • Evolved from pressure and anticipation.
  • Every organ has its biological clock.
  • Its performance varies during the day.
  • Babies also have clocks, but they aren’t tied to outside light until 6 months.
  • Today’s top diseases are chronic.
    • They can be caused by an unhealthy circadian clock.

How is it related to our metabolism?

  • After many experiments on rodent’s brain
  • Without it, we would have no sense of time.
  • It synchronises organs to activate during certain times.
  • What happens in the case of neurodegenerative diseases?
    • The SCN is damaged by the degeneration.
    • People lose their internal clock.
    • The hippocampus, which is in charge of long-term memory, is affected.

The importance of light

  • Light can reset our internal clock.
    • It adapts when seasons change and when we travel in other time zones.
  • Why is it blind people can’t see, but still have a clock?
    • Scientist found that if the eyes are taken, they loose their clock.
    • They discovered melanopsin, a photoreceptor, in the ganglion cells, located in the eyes.
    • These photoreceptors are connected to our SCN.
    • They are sensitive to BRIGHT light and TIME of exposure (10 000 Lux during several minutes).
  • Melanopsin also regulates sleep and our mood.
    • It suppresses melatonin, a sleeping hormone.
    • Melatonin they builds up during the day as the light decreases, making us sleepy when night comes.
    • When the sky is gray/there’s no light it can cause sessional depression.
    • We need more light in the first half of the day and less after noon.
    • Melanopsin promotes cortisol, an hormone that makes us more alert (stress hormone)
    • Therefore, cortisol spikes early in the morning and decreases throughout the day.
    • Leading a stressful life maintains our level of cortisol high, which can lead to health issues.

The role electronics play in our internal clocks

  • Blue light from screens and lighting send the wrong signal to the SCN.
  • Melatonin can’t build up.
    • So, someone would have trouble sleep or would wake up tired.
  • Philips Hue: Lights that can be programmed to send red lights instead of blue.
  • F.lux: Application that filters blue light and sends different shades depending on the time of day.

What about Jet Lag and night workers?

  • People that switch from a day shift to a night shift:
    • They sleep during the brightest sunlight exposure.
    • They rarely get exposed to the natural light.
  • While light does half of the work, the other half is done by food.
  • When traveling, light and food habits change, which messes up our SCN.

How food regulates our tissues

  • Internal clocks are like traffic lights: without the right timing, it creates accidents and traffic jams.
  • There’s a specific time for every metabolic activity.
  • If not properly adjusted:
    • There’s build up of undesired by-products.
    • It puts stress on our cells.
    • It can lead to many chronic diseases.
  • Our organ’s clocks respond to when we eat.
    • The act of eating turns on the genes responsible for digestion.
    • Light has little impact in that case.

The principle behind time-restricting feeding

  • The idea is to restrict your eating into a certain period of time, usually being12h.
  • Mice that don’t have a circadian clock have greater chances of developing a metabolic disorder such as:
    • Obesity
    • Cardiovascular diseases
    • Diabetes
    • Cancer
  • High fat diet and high sugar diet were tested with time-restriction.
    • Did not matter WHAT or HOW MUCH you eat but WHEN you eat is crucial.
    • Mice ate the same food but the ones on time-restriction had 28% less body mass and 70% less fat.
  • Time restricting has a huge impact on our body.
  • Nutrition or quality of food still matters.
  • The program increased lean mass.
    • This can be caused by an increase in Nicotimamide Ribose, which creates more NAD.
    • More NAD gives more ATP.
    • ATP, being the main energy source of our body, boosts our energy level.
  • Restricting in an 8h to 9h period is even more beneficial.
    • It increases endurance.
    • An increase in brown fat tissue was noted.
    • There’s also an increase in mitochondria activity.

Intermittent fasting versus time-restricting feeding

  • In both cases, there’s a prolonged fasting period.
  • When we eat, we damage our cells.
  • Fasting promotes repairs.
  • Intermittent fasting restricts calories, time-restricting does not.
  • It’s a comeback to our primordial physiology.
  • The two methods are in synch with the circadian clock.
  • Melatonin receptors were found in pancreas.
    • The increase of melatonin that happens during the day inhibits insulin production.
    • Therefore, late night calories have different effect on our health.
  • mycircadianclock.org
    • This site is a nutrition study application.
    • 50% of the population eat throughout a period of 15 hours.
    • 8 people that were asked to restrict their time.
      • They lost 4% body weight.
      • They slept better and were more energetic in the morning.
    • It’s an indirect way to reduce calories and eat better.
    • It contains two phases:
      • Phase 1: Collect how much and when people eat, sleep, exercise.
      • Phase 2: Selecting a program to follow.
    • It can be synched with the Health Kit and Google Fit application, which measure movement.
  • It’s a simple life style changes.
  • Experiments on fruit flies showed:
    • Their heart has similar genes and diseases as humans.
    • By following a time-restricted diet, they develop heart problem later.
    • They slept better and were more energetic.
    • The mitochondria in the heart cells were healthier.
    • The Electron Transport Chain (ETC) was more effective.
    • It also showed better proteostasis, which is important for protein folding.

Links to microbiota and digestion

  • Our microbiota also follows a circadian clock.
  • Different bacteria are active during different part of the day.
  • Regularity between fasting and eating allows a vast variety of species to grow.
  • Time-restricting changes the way sugar are digested.
  • It can also decrease our cholesterol level and increase the production of bile acid.
  • uBiome: a website where you can evaluate the changes in your gut bacteria.