Modified Fasting Gets You 80% of the Benefits at 50% of the Difficulty (Here’s What You Can Actually Eat)

Dr. Jason Fung, bestselling author of The Complete Guide to Fasting and The Obesity Code, recently sat down to share how his thinking on fasting has evolved as new research emerges.

What he revealed might surprise even the most dedicated fasters.

Longer fasts—and modified approaches that make them easier—are showing benefits that go far beyond weight loss.

From inflammation reduction to cancer prevention, the science is painting a compelling picture of fasting’s therapeutic potential.

The Three-Day Threshold: When Deeper Benefits Begin

Extended fasting triggers biological changes that shorter fasts simply can’t match.

Dr. Fung pointed to a groundbreaking seven-day water fast study that measured protein expression throughout the body. The findings were striking: massive beneficial changes in markers related to heart disease didn’t appear until day three.

They did a 7-day water fast and what was interesting is they measured all these proteins and there’s a humongous change in the protein expression in the body. And mostly hugely beneficial in terms of heart disease and so on. Like massive benefits. And a lot of them, interestingly they point out in the study, don’t actually happen until day three.

This discovery challenges conventional wisdom around popular intermittent fasting protocols like 16:8 or even 24-hour fasts.

While those approaches offer metabolic benefits, pushing past the 72-hour mark appears to unlock an entirely different level of cellular transformation.

Modified Fasting: The 80/20 Solution

Water-only fasting isn’t the only path to these benefits, and that’s game-changing news for most people.

Dr. Fung now advocates strongly for modified fasting protocols—approaches that allow limited calories while maintaining most of fasting’s therapeutic effects.

These include Dr. Michael Mosley’s 5:2 diet (five days normal eating, two days at 500 calories) and Dr. Valter Longo’s fasting mimicking diet (five days at 800-1,000 calories with specific macronutrient ratios).

My thinking is that you sort of get like 80% of the benefits, but it’s 50% easier, right? So, then you’re still talking about a huge plus side, right? Compared to water only fasting.

Research on modified fasting now extends beyond diabetes and weight loss into inflammatory conditions and even cancer prevention.

These studies weren’t available when Dr. Fung first wrote about fasting, fundamentally shifting how practitioners can recommend the practice.

Debunking the American Heart Association Controversy

Not long ago, headlines claimed that fasting for just eight hours increased heart attack risk by 91%.

Dr. Fung didn’t mince words about this American Heart Association announcement.

The American Heart Association had this big thing about how if you fasted for 8 hours, your heart risk went up by 91% or something like that. That’s the stupidest thing ever, right? Like can you even believe that? That’s such crap, right? It was ridiculous.

That widely circulated claim suggested even 12-hour fasts—essentially normal overnight eating patterns—raised cardiovascular risk by 66%.

However, research on time-restricted eating and cardiovascular health shows more nuanced results. While some observational data has raised questions about very narrow eating windows in certain populations, the overall body of evidence linking moderate fasting practices to heart disease remains limited and contested among experts.

Doctors fielding patient concerns found themselves reassuring worried fasters that decades of human evolution wouldn’t have produced a metabolic system destroyed by skipping breakfast.

Fasting Aids and Training Wheels

The key to successful extended fasting isn’t white-knuckling through hunger—it’s strategic support.

Dr. Fung and his clinical partner Megan Ramos have always recommended modifications including teas, coffees, and bone broth during fasting windows. Now, their approach has expanded further based on emerging evidence.

Approved fasting aids include:

• Bone broth (provides sodium, minerals, and minimal protein)
• Avocado (high fat, low carb and protein)
• Olives (similar macronutrient profile)
• Small amounts of nuts (watch protein content)
• Black coffee and unsweetened tea

Research suggests these “fasted snacks” can actually extend fasting duration by making it tolerable, leading to greater overall metabolic benefit than shorter water-only fasts.

One study Dr. Fung referenced compared 15-hour fasts to 17-hour fasts where participants consumed a low-calorie, low-protein snack at the 15-hour mark. The extended group continued experiencing metabolic improvements—weight loss, lower glucose, and reduced insulin—that the 15-hour group didn’t achieve.

The Science Behind Modified Approaches

What makes modified fasting work comes down to nutrient sensing.

Your body detects incoming nutrients primarily through two pathways: insulin (responding to carbohydrates) and mTOR (responding to protein).

When you turn off those nutrient sensors, the body senses, “Hey, no nutrients are coming in.” So, you’re going into this sort of quiescent, restful sort of state where you’re sort of rebuilding, you know, sort of resting rather than building, right?

This explains why Dr. Valter Longo’s fasting mimicking diet specifically limits both carbohydrates and protein—keeping both insulin and mTOR suppressed even while consuming calories.

Foods high in fat but low in carbs and protein don’t trigger these nutrient sensors significantly, allowing the body to remain in a fasted metabolic state.

The Avocado-Bacon Protocol

One approach Dr. Fung’s clinic developed—initially met with skepticism—was the “avocado bacon diet.”

Participants consumed only bacon and avocado for several days, keeping protein moderate, carbs minimal, and insulin low.

Because it wasn’t a complete fast, people could sustain it longer than water-only protocols. Yet they still achieved net metabolic benefits that exceeded what they would have gained from a shorter, stricter fast.

It’s like you take a little bit, but then you extend it a little bit further. So, you’re actually getting more benefit than if you didn’t take it at all, right?

This principle—trading perfect restriction for sustainable duration—represents Dr. Fung’s evolved thinking on practical fasting implementation.

Breaking Through the 24-Hour Barrier

One meal a day (OMAD) represents a 24-hour fast between meals, but pushing to 36 hours creates a qualitatively different experience.

Dr. Fung noted something fascinating about crossing this threshold: by the second morning after beginning a fast, hunger resets completely.

People wake up feeling lighter and better, not desperately hungry as they might expect. Everything normalizes—you’ve simply skipped an entire day of eating without the difficulty that initial transition period creates.

This reset phenomenon makes subsequent fasting days significantly easier than the first 24 hours.

Targeting Visceral Fat

Not all body fat poses equal health risks, and fasting specifically attacks the dangerous kind.

Subcutaneous fat (under the skin) carries minimal metabolic consequences. Visceral fat (around organs) drives insulin resistance, inflammation, cardiovascular disease, and metabolic syndrome.

Fasting and low-carbohydrate approaches preferentially mobilize visceral fat through a specific mechanism.

When you consume excess carbohydrates, your liver converts glucose to fat through de novo lipogenesis. Unable to store all this manufactured fat, the liver exports it as VLDL triglycerides, depositing fat around organs—in the pancreas, around the heart, throughout the abdominal cavity.

This explains why metabolic syndrome presents as a cluster: high blood sugar, elevated triglycerides, low HDL, and abdominal obesity all stem from hyperinsulinemia and excessive de novo lipogenesis.

The Liver Shrinking Effect

Surgical teams have known for years that preoperative low-calorie, low-carbohydrate diets dramatically shrink fatty livers, making abdominal surgery safer and easier.

CT scan studies show five days of this dietary approach reduces liver fat by approximately 28% while total body fat drops only 1%.

What it’s telling you is that you’re preferentially pulling out that fat from the viscera, which is exactly what you want to do, right? Fasting is a super good way to do that.

When you deplete liver glycogen through fasting or carbohydrate restriction, your body must mobilize stored fat for energy—and it draws first from the liver and surrounding visceral deposits.

Fasting and Cancer: A Metabolic Strategy

Cancer cells exhibit a metabolic vulnerability that fasting exploits.

Insulin functions as a growth hormone, and many cancer cells express far more insulin receptors than their healthy counterparts. Breast cancer cells, for example, have six to eight times more insulin receptors than normal breast tissue.

These cancer cells avidly consume glucose, thriving in high-insulin, high-glucose environments.

So, what’s a good strategy? Well, how about lower insulin? It’s like that seems to make sense. How are you going to do that? Well, fasting is good, right?

Most healthy tissues can run efficiently on either glucose or fat. Cancer cells struggle with fat metabolism—they can use it, but prefer glucose.

Fasting and ketogenic diets lower circulating glucose and insulin, essentially starving cancer cells of their preferred fuel while healthy cells adapt easily.

While evidence for fasting’s role in cancer treatment remains preliminary and observational data linking obesity to certain cancers is well-established, controlled trials specifically testing fasting as a cancer intervention are still limited. Most existing research involves animal models or small human studies, making definitive conclusions about clinical efficacy premature.

Dr. Fung emphasized he would never recommend avoiding conventional cancer treatment, but views fasting as a powerful adjunctive strategy during chemotherapy.

The Muscle Loss Myth

Perhaps no fasting concern generates more anxiety than fears about losing muscle mass.

Dr. Fung considers this worry fundamentally misguided, based on faulty reasoning about how the body actually works.

Why would your body store energy in the form of glucose in the form of fat? And when you need it, you use your protein. Like that seems pretty stupid. Why would you think the human body is just so stupid, right?

Muscle gain and loss respond primarily to use, not feeding status.

Astronauts in zero gravity lose muscle rapidly regardless of nutrition. Bedridden patients experience muscle wasting even with adequate protein intake. Conversely, people who exercise during fasting maintain and even build muscle.

From an evolutionary perspective, the alternative makes no sense. If fasting caused muscle loss while preserving fat, our ancestors would have become progressively weaker and fatter during food scarcity—hardly a survival advantage.

The body stores energy as fat precisely because it’s an efficient reserve. Breaking down functional muscle tissue while fat reserves remain would be metabolically absurd.

Muscle loss during fasting occurs only in extreme circumstances—when body fat drops to around 4% and no other energy reserves remain.

The Protein Powder Marketing Lie

Dr. Fung reserved particular criticism for the protein supplementation industry.

People think, “Oh, I want to build muscle. I’m just going to eat protein.” You don’t gain muscle by eating protein. You gain muscle by exercising, okay?

The notion that consuming protein powder automatically builds muscle—independent of resistance training—defies basic physiology.

Yet marketing has convinced millions to maximize protein intake through ultra-processed supplements, from protein-fortified Doritos to protein water.

While protein plays important roles—particularly in satiety—the idea that more protein equals more muscle represents pure marketing fiction.

The Critical Refeed Window

Breaking a fast thoughtfully matters, though perhaps not for reasons people assume.

Dr. Fung recommends focusing on unprocessed or minimally processed whole foods, emphasizing proteins and fats while moderating carbohydrates.

Since no essential carbohydrates exist (unlike essential amino acids and fatty acids), prioritizing protein and fat ensures you’re meeting true nutritional needs.

The refeed window becomes particularly important for those doing fasted exercise.

Growth hormone increases during fasting, priming the body for muscle synthesis when feeding resumes. Breaking your fast with nutrient-dense foods maximizes this anabolic window.

Practitioners working with fasting communities notice that people who refeed with fiber-rich, protein-adequate, healthy-fat meals experience reduced food noise and sustained weight loss compared to those who break fasts with high-carbohydrate foods.

The Bone Broth Solution

Traditional bone broth has always played a central role in Dr. Fung’s fasting protocols.

Simmered bones release collagen, hyaluronic acid, minerals, and approximately 12 grams of protein per serving with virtually zero fat—an ideal macronutrient profile for modified fasting.

The minerals, particularly sodium, help prevent the fatigue and weakness some people experience during extended fasts.

The practical challenge? Traditional bone broth requires 18-24 hours of simmering, plus cooling time to skim fat—easily a two-day process.

Dr. Fung addressed this by developing Aera bone broth, a powdered version with a single ingredient: chicken bones. No fillers, no additives, just dehydrated bone broth that reconstitutes in five minutes.

It’s a total game changer in my opinion for fasting. I don’t make bone broth anymore. I actually just use this stuff because it’s like why do I even bother?

Beyond convenience, powdered bone broth offers significant cost advantages. Jarred bone broth often runs $7-8 per cup; the powdered version costs approximately $1.50 per serving.

Users can customize their bone broth by adding salt to preference, simmering with vegetables for flavor, or stirring in miso paste.

Practical Implementation: Five Days Modified vs. Three Days Water-Only

When asked about optimal fasting duration for full-body reset, Dr. Fung offered two equivalent approaches.

Water-only fast: Three days to begin seeing the deeper protein expression changes identified in recent research.

Modified fast: Five to seven days using fasting aids like bone broth, avocado, olives, or the fasting mimicking diet approach.

The analogy Dr. Fung used: sprinting versus distance running. You can go hard and fast with water-only for three days, or ease the intensity and extend duration with modifications for five to seven days.

Both paths lead to similar metabolic destinations—deep cellular cleanup, reduced inflammation, visceral fat mobilization, and the protein expression changes that don’t appear in shorter fasts.

Sustainable Practice Over Perfect Execution

Dr. Fung’s evolved perspective emphasizes one principle above all others: adherence beats intensity.

If you hated every time you have to do a fast, then very soon you’re going to stop. There’s no reason to continue. So, by making it easy enough that it’s not a huge impediment, you’re going to be able to keep doing it longer, which is no small thing. It’s actually most of the battle.

This represents a significant philosophical shift from purist approaches that insist on water-only protocols.

If modifications help someone complete regular five-day fasts throughout the year versus struggling through one miserable three-day water fast and never trying again, the modified approach delivers vastly superior long-term results.

Success comes not from white-knuckling through the most restrictive protocol possible, but from finding an approach sustainable enough to become a regular practice.

Key Takeaways for Modern Fasters

Dr. Fung’s updated recommendations synthesize years of clinical experience with emerging research:

• Aim for 3-7 day fasts to access deeper metabolic benefits that don’t appear in shorter windows
• Use fasting aids strategically—bone broth, avocado, olives, coffee, tea—to extend duration comfortably
• Don’t fear muscle loss unless body fat is already extremely low; continue resistance training during fasts
• Focus refeeds on whole foods emphasizing protein, healthy fats, and fiber rather than processed carbohydrates
• Target visceral fat specifically through fasting and low-carb approaches that deplete liver glycogen
• Consider fasting as adjunctive therapy for inflammatory conditions, metabolic disease, and cancer prevention
• Push past 24 hours to experience the hunger reset that makes extended fasting surprisingly tolerable
• Prioritize sustainability—an “imperfect” modified fast you’ll actually do beats a perfect water fast you’ll abandon

As research continues expanding our understanding of fasting’s therapeutic mechanisms, one thing becomes increasingly clear: the practice offers far more than weight loss.

From cellular cleanup to inflammation reduction, from visceral fat mobilization to potential cancer prevention, fasting represents one of the most powerful metabolic interventions available.

The key is making it work for you—not forcing yourself into rigid protocols that become unsustainable burdens.