How to Optimize your Health with Intermittent Fasting
Now that we’ve made it through Thanksgiving, let’s talk about one of my favorite topics: intermittent fasting (IF) or time-restricted feeding (TRF)...
There’s currently a lot of hype around IF/TRR. Everyone in the health space seems to be talking about it. And there’s good reason; there is now extensive literature purporting its benefits.
Caveats:
Let me preface this topic by saying IF/TRF is not for everyone (i.e. children, pregnancy, during breastfeeding, history of eating disorder, other populations who have higher nutrient needs, etc.).
While IF/TRF is concerned with WHEN you eat, it’s still important to be concerned about WHAT you eat. A clean, healthy whole foods diet is essential to get the full benefits of IF/TRF. And I would also emphasize, exercise/movement is equally important to achieve these benefits.
What is IF/TRF?
“The best of all medicines is resting and fasting” - Benjamin Franklin (1706-1790)
The human body is filled with inherent repair systems that will naturally turn on in certain circumstances. From autophagy (removing damaged cells) to activating Natural Killer (NK) cells, to neuroplasticity and stem cell proliferation, the emerging science surrounding the body's natural ability to heal and rejuvenate with IF is exciting.
Intermittent fasting really means “tightening up your eating window.” This can be done with great variation in timing and cycles. The basic premise is to optimize the process of switching between our feast (eating) and famine (fasting) state.
Emphasis: IF is not a diet – it’s a protocol that involves extending your natural fasting period.
The History of Fasting
Fasting is not a new concept. Records show that it was used way back in 360 BC by Hippocrates in ancient Greece to improve health. However, fasting protocols seem to have been forgotten in modern times, until now.
No matter where we look in the world, there are different forms of fasting traditions, from Lent in Catholicism to Ramadan in Islam. Fasting is a protocol that has been used by humans since the beginning of time.
In Asia, fasting is known as "zhai" or "zai", which means both "vegetarian" and "fasting." Many people believe that removing indulgences from the diet (i.e. foods that are only eaten for taste) brings about spiritual merit and physical well-being. Buddhists also take part in daily and prolonged fasts for moral and spiritual reasons.
What are the benefits of IF?
Many studies have shown IF/TRF:
increases insulin and leptin sensitivity and improved hemoglobin A1C (i.e improved glucose regulation)
reduces overall body fat and waist circumference
improves resting heart rate and blood pressure while increasing heart rate variability
improves CRP (C Reactive Protein, a biomarker for inflammation) and thus reduces chronic inflammation
improves joint pain
reduces stress-related damage to the brain and heart
reduces free-radical production
reduces risk of diabetes
improves cellular function and regeneration
improves mitochondrial health and supports DNA repair
increases antioxidant defenses
improves biomarkers for breast cancer risk
improves cognitive function (memory, learning, verbal fluency, executive function)
increases autophagy (removing damaged and dysfunctional cells to make room for properly functioning cells)
increases BDNF, brain-derived growth factor (which reduces risk of depression)
reduces TMAO (trimethylamine N-oxide), which impacts microbiome markers for cardiovascular disease
improve muscle mass decline with age
positively influences genes that play a modulatory role in anti-aging and longevity (BMAL1, CLOCK and sirtuins, SIRT1 and SIRT3)
IF/TRF leads to systemic cellular responses that also carry over into the eating hours too. During fasting, cells activate autophagy defense pathways (removing and repair damaged molecules), and during the feeding hours, these responses continue to activate cell growth, plasticity, and regeneration. This also includes reduction of mTOR (mammalian target of rapamycin) pathway activity, which further up-regulates autophagy.
And when combined with exercise, benefits are enhanced. The combination of IF/TRF and exercise increases our ATP (energy currency) and stimulates mitochondrial biogenesis and mitochondrial stress resistance, resulting in improved exercise performance.
How does IF work?
IF/TRF works via utilization of glucose as fuel to fatty acid-derived ketones, (i.e. fat storage to fat mobilization). Timing of ketosis can vary by individual. Flipping the switch from glucose to ketones confers many health benefits because ketone bodies are a far more efficient energy source than glucose, and ketones do not generate as much reactive oxygen species as glucose does.
There are many metabolic mechanisms that fuel the benefits of intermittent fasting. Fluctuating between using ketones (fat) for fuel and glucose (sugar) is known as “metabolic switching” and has been found to make the body more flexible in what fuel source it uses.
How do you start IF?
I recommend most people start off gradually with an overnight fast of 10-12 hours, working up to a goal of 14-16 hours. Listen to your body. I find intuitive fasting works better than going “all in.”
In the IF/TRF world, people speak of eating and fasting “windows” as follows:
Eating window: When you consume all food and calories for the day.
Fasting window: When you abstain from food and only consume water (or include a “dirty fast,” which essentially means eating specific nutrients that can still keep you in the fasting state (like MCT Oil).
IF/TRF is done repeatedly over a condensed timeframe. The most famous being the 5:2 or 8:16 methods, as outlined below:
5:2/Alternate Day - Eat normally for 5 days; fast for 2 days every week.
8:16 - Eat all food during an 8 hour eating window; fast for 16 hours every day.
14:10 - eat all food in 10 hours and fast for 14 hours.
OMD (one meal per day) - 24 hour fast, which I recommend starting at only doing 1-2 times per week (i.e. dinner to dinner).
Fasting Mimicking - consuming ketones, which tricks your body into quickly getting into ketosis. A fasting-mimicking diet is designed to make the body think that it’s fasting, when it’s not.
Additionally, when following an IF/TRF protocol you can eat the same amount of food and don’t have to count calories.
Why Dieting and Exercise Alone Doesn’t Work
Energy is normally created from blood sugar and glycogen (stored glucose in muscles and the liver). When we eat, we replenish these stores. Fat remains untouched as we continually replenish our glycogen stores. Additionally, as we age, our bodies don’t utilize fat stores as efficiently, making it harder to use fat for fuel later in life. It takes up to 8 hours for glycogen stores to fully metabolize. Once glycogen is depleted, the body will turn to burning fat for fuel. The human body will only metabolize fat stores as a last resort (after approximately 8 hours of fasting) - making IF the go-to remedy for weight loss.
How does IF play into longevity?
Data shows IF/TRF exerts its anti-aging effects by influencing the entire family of CLOCK and BMAL1 genes and sirtuins, which are modulators of aging, age-related diseases, and the circadian system.
We often think of the physiology of the human circadian rhythm as it relates to the cycling of light and dark. However, the timing of feeding and fasting over a given 24-hour period also profoundly influences the physiology of our circadian rhythm through interactions with nutrient-sensing pathways in the body. Circadian rhythms work via an oscillating genetic network that operates on a roughly 24-hour cycle. Dysfunctional genetic expression in the circadian system can negatively impact metabolic function and increase the risk of obesity, heart disease, diabetes, cancer, and accelerated aging. Gene expression studies demonstrate that IF/TRF supports circadian rhythm and metabolic homeostasis.
Sirtuin genes play a key role in oxidative stress, as well as enhanced health and longevity. In addition, SIRT1 in particular regulates the circadian clock genes BMAL1 and CLOCK. Research demonstrates that the sirtuins, specifically SIRT1 and SIRT3, are activated by fasting.
How do you make IF work with your lifestyle?
From a clinical perspective, the key appeals of IF/TRF are high compliance and easy sustainability. For one to get the long-term health benefits of IF/TRF, this eating style should become more of a way of life versus a quick-fix, short-term diet strategy.
The benefits of IF/TRF correlate to eating in accordance with how our bodies naturally operate.
It’s all about ROI - return on investment. And I have found this approach, which is FREE and nicely takes out some of the brainspace of time spent meal planning, seems to really work for me and for many of my patients.
And if you want to get really nerdy, get a continuous glucose monitor (CGM) to follow your progress. I often prescribe the Freestyle Libre continuous glucose monitor, which is a 2 week sensor you wear on your arm for around 35 dollars (download the Freestyle Libre app as your reader device). This can help identify trends with your blood sugar control.
There is no one food approach that fits all, but if you’re looking for something that is a sustainable way to lose weight, increase mental clarity, improve metabolic function and overall health and longevity, this can be a great approach. Give it a try!
Other Resources I Like:
“Fast This Way” by Dave Asprey
“Intuitive Fasting” by Dr. Will Cole
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