There’s finally some consensus in the nutrition field about fasting. We now know how to practice it to provide the most benefits for our energy levels, blood sugar control, and weight loss. In this blog post, I’m going to explain the exact strategy I share with my patients to achieve these results.
Table of Contents
Section 1: The Emerging Consensus
1.1 Fasting Controversy and Rodent Studies
1.2 Autophagy in Rodents and Humans
1.3 Human Evidence on Time-Restricted Eating
Section 2: The Right Way to Fast (What I Tell My Patients)
2.1 Meal Timing for Optimal Health
2.2 Practical Tips for Intermittent Fasting
2.3 Summary of the Best Fasting Approach
The Emerging Consensus
To understand how we arrived at the current consensus, we need to explore the fasting controversy and the mistakes made along the way.
1.1 Fasting Controversy and Rodent Studies
The initial excitement about fasting primarily came from studies on rodents, where calorie intake was restricted to a small window each day. Scientists noted weight reduction, improved blood sugar control, lower insulin levels, and an increased lifespan in these animals. The critical point was that even when total food intake was matched to a control group, the rodents still experienced these benefits [1].
Why does that last point matter so much? Previous rodent studies had already shown that restricting calories can extend rodent lifespan. So one might suspect that the shorter eating window simply led to fewer calories consumed, which would explain the benefits. But in these new time-restricted feeding studies, both groups of rodents ate the same amount of food. The difference was simply that one group ate all its food within a shorter time window each day. This observation fueled the popularity of time-restricted feeding, often referred to as “intermittent fasting.”
Even for those who don’t need to lose weight, it was hoped that if humans also ate within a small timeframe, we could enjoy similar benefits, including possible lifespan extension [2].
If you know someone who has tried intermittent fasting, consider sharing this post with them. They’ll likely find these insights extremely helpful.
But do humans experience the same benefits as rodents when restricting their eating to a shorter period each day?
1.2 Autophagy in Rodents and Humans
When rodents were in a daily fasting period, scientists took biopsies and found that autophagy was occurring in their cells [3]. Autophagy is a cellular “cleanup” process that clears away old, damaged components so they can be replaced by new, healthy components. The evidence suggests that autophagy can play an essential role in extending lifespan.
That certainly sounds exciting, but here’s the catch: humans are not rodents. Human clinical trials have not yet conclusively demonstrated that time-restricted eating triggers autophagy in people the same way it does in rodents. One likely reason is that rodents have very different metabolic systems. You’ve probably heard the term “dog years,” meaning dogs age faster than humans. Similarly, rodents age much more quickly than humans. Research suggests that one rat day is roughly equivalent to 27 human days [4].
In other words, the few hours that rodents fast may be metabolically equivalent to days of fasting for humans. Furthermore, our bodies store energy as glycogen in our livers, and it can take up to 48 hours to deplete glycogen sufficiently to meaningfully activate autophagy [5].
So, while the autophagy effect in rodents is promising, humans may need a different fasting duration altogether to reap comparable cellular cleanup benefits.
1.3 Human Evidence on Time-Restricted Eating
So, if time-restricted feeding doesn’t necessarily guarantee the same autophagy benefits for us, what about weight loss and blood sugar control?
Initially, it looked quite promising. A 2020 meta-analysis suggested time-restricted feeding offered greater weight loss and reductions in blood sugar levels than diets in which there were no set eating windows [6]. That seems to confirm the rodent studies. However, there is a crucial problem: in most time-restricted feeding studies involving humans, the group that restricted eating windows also ate fewer calories than the control group. They naturally ended up consuming less food, likely because there was less opportunity to snack [6].
To truly isolate the effect of time restriction from total calories, we need studies that match calorie intake in both groups. This is precisely what the Cochrane organization did in their 2021 meta-analysis [7]. They found that in studies where calorie intake was kept the same between the intermittent fasting group and the control group, there were no substantial differences in weight loss or blood sugar levels.
In other words, any benefits from time-restricted feeding really come down to the fact that people end up eating fewer calories. Simply eating within a smaller window of time—without reducing calories—doesn’t provide extra “magic.” So if the shorter eating window can help people cut down on overall calorie consumption, that may be where its real value lies.
Yet, there is an important element of meal timing we still need to explore, especially regarding energy levels. And that’s where some other problems with fasting come in.
1.4 Three Big Fasting Mistakes
Mistake #1: Multiday Fasts and Muscle Mass
A growing body of evidence reveals that as muscle strength declines, overall mortality increases. Muscle mass is key here. One study concluded that declining muscular strength is independently linked to higher all-cause and cardiovascular mortality, even when adjusting for age, body fat, and other factors [8].
On average, people lose about 1% of their muscle mass per year starting at age 40. We definitely don’t want to accelerate that loss [8].
When I first tried multiday fasts, I personally experienced rapid muscle loss. It took considerable effort to regain that muscle, only to lose it again during my next extended fast. Therefore, I advise against multiday fasts because of the negative impact on muscle mass.
Mistake #2: Missing Protein While Fasting
Even shorter fasts can subtly threaten muscle mass if we’re not careful with our protein intake. To support muscle building and maximize the benefits of exercise, we ideally want around 1.6 grams of protein per kilogram of body weight per day [18].
People who practice time-restricted feeding often skip breakfast and only eat in the afternoon and evening. While this does limit calories, it can also limit protein intake, potentially undermining muscle maintenance.
Mistake #3: Skipping Breakfast and Eating Late
Finally, there’s a significant issue with most time-restricted eating plans: they skip breakfast. Research has shown that people who consume only one meal a day, usually in the evening, tend to have higher morning blood glucose levels and a delayed insulin response [10]. This suggests reduced insulin sensitivity, something we want to avoid.
Another study comparing morning vs. evening meal processing concluded that our bodies handle food better in the morning, with lower post-meal blood sugar levels [11]. Additional research discovered that a morning meal seems to stimulate more calorie burning than the same meal eaten at dinner [12]. Our circadian rhythms play a critical role in how we metabolize food, and eating more in the morning aligns better with our natural biological clock [13].
Moreover, when we eat late at night, our sleep quality may suffer. Eating a big meal shortly before bedtime often makes it harder to fall asleep or stay asleep. Observational data show that people eating or drinking within an hour of bedtime are more likely to experience reduced sleep quality and prolonged periods of wakefulness at night [14]. A clinical study similarly found that late-night eating impairs several markers of good sleep [15].
A poor night’s sleep has ripple effects on our energy and mood the next day. By contrast, having an early, light dinner allows our bodies to focus on repair and restoration, often leading to noticeably improved energy levels in the morning.
Skipping breakfast also raises concerns about blood sugar control, since our insulin sensitivity is highest early in the day [16]. Additionally, research indicates that late-night snackers often choose foods high in saturated fat, sugar, and salt, which can worsen health outcomes over time [17].
Putting all this together, we see that while time-restricted feeding can help reduce total calorie intake—and thus support weight loss—it can also cause problems if we’re not mindful of meal timing, protein intake, and muscle maintenance.
The Right Way to Fast (What I Tell My Patients)
Now that we’ve explored the pitfalls, let’s discuss how to harness intermittent fasting or time-restricted eating in a way that boosts energy, regulates blood sugar, and supports healthy weight management.
2.1 Meal Timing for Optimal Health
First, the actual length of the “eating window” (e.g., 8 hours vs. 12 hours) may not be as critical as many believe. It’s still a useful tool for reducing caloric intake, but the key is when that window falls. Specifically, finishing meals earlier in the evening appears to be a game-changer. Avoiding late-night meals helps us sleep better, leading to higher energy levels the next day. It also helps stabilize blood sugar and can reduce the likelihood of binge-eating calorie-dense snacks.
If my goal were to lose weight, I might compress my eating window so that it’s easier to eat fewer calories overall. But I also make it a priority to ensure I finish my day’s last meal earlier rather than later.
2.2 Practical Tips for Intermittent Fasting
Here is how I guide my patients:
1. Eat Most of Your Calories Early
Our bodies process food best in the morning and midday, when insulin sensitivity is higher. In many cultures, however, breakfast is light or even skipped, with dinner being the heaviest meal. I urge my patients to reverse this. A simple mantra is: "Breakfast like a king, lunch like a prince, and dinner like a pauper."
2. Light, Early Dinner
Try not to eat late into the evening. Stop eating at a set time, say 6 or 7 p.m. Then, wait about 30 minutes and brush your teeth to signal to yourself that the kitchen is closed. By the time bedtime rolls around, your digestive system isn’t working overtime, which often leads to higher-quality sleep.
3. Protein Intake Is Crucial
For those who try to keep their eating to, say, an 8-hour window, hitting protein targets can be more challenging. To keep muscle losses at bay, I advise looking carefully at overall protein intake. A low-calorie protein shake during the fasting window can be helpful, even if it slightly “breaks” the fast, so long as total calories remain in check. This approach ensures you’re getting about 1.6 grams of protein per kilogram of body weight per day [18].
By applying these principles, I’ve seen patients improve not just their metabolic markers—like fasting blood glucose levels—but also their day-to-day energy. This is likely a combination of better sleep, more stable blood sugar, and adequate protein intake for muscle preservation.
2.3 Summary of the Best Fasting Approach
To recap, we now have a clearer understanding of how to avoid the common pitfalls of fasting while reaping its benefits:
1. Avoid Multiday Fasts
They can lead to muscle loss, which is counterproductive for long-term health and longevity.
2. Prioritize Protein
Especially when restricting the eating window, ensure you still reach a protein intake of around 1.6 g/kg/day to protect and maintain muscle mass.
3. Don’t Skip Breakfast; Skip Late Dinners Instead
Capitalize on your body’s higher insulin sensitivity and metabolic efficiency in the morning. Finish your day with a lighter meal, earlier in the evening, to support better sleep and healthier blood sugar levels.
These steps help people lose weight more easily (by reducing caloric intake), stabilize blood sugar, and experience noticeably higher energy levels throughout the day. By aligning with our natural circadian rhythms, we harness our body’s inherent strengths in digestion and metabolism during earlier hours, which translates to better overall health.
Reference List
1. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6627766/
3. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2990190/
4. https://pmc.ncbi.nlm.nih.gov/articles/PMC5355425/
5. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC8151159/
6.https://iris.unito.it/retrieve/handle/2318/1739566/635675/Bo%20et%20al%20Revised.pdf
8. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5772850/
9. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6322506/
10. https://pubmed.ncbi.nlm.nih.gov/17998028/
11. https://pmc.ncbi.nlm.nih.gov/articles/PMC6266071/
12. https://www.nature.com/articles/ijo2015138
13. https://pmc.ncbi.nlm.nih.gov/articles/PMC5657289/
14. https://pubmed.ncbi.nlm.nih.gov/34511160/
15. https://pmc.ncbi.nlm.nih.gov/articles/PMC3227713/
16. https://pmc.ncbi.nlm.nih.gov/articles/PMC6266071/
17. https://pmc.ncbi.nlm.nih.gov/articles/PMC10799113/
18. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5867436/
