Intermittent fasting, particularly the 5:2 diet, has taken the world by storm, promising weight loss, improved metabolism, and even longevity.
The concept is simple: feast for five days, fast for two. For many, it’s an easier alternative to restrictive daily dieting.
But here’s where things get interesting.
A new study suggests that the benefits of intermittent fasting might go far beyond weight loss.
Researchers from the University of Florida and Harvard Medical School found that fasting triggers powerful cellular responses that could boost longevity and improve metabolic health.
However, they also stumbled upon a surprising roadblock: adding antioxidant supplements to the mix might actually cancel out these benefits.
“The hypothesis is that if the body is intermittently exposed to low levels of oxidative stress, it can build a better response to it,” said Martin Wegman from the University of Florida College of Medicine.
This means that something many of us assume is “healthy”—taking antioxidant supplements—could actually work against the benefits of fasting.
So what’s really happening inside your body when you fast?
And why might popping that vitamin C pill be a mistake? Let’s break it down.
How the 5:2 Diet Works—and Why It’s So Popular
The 5:2 diet, often called the “feast-or-famine” diet, gained popularity because it offers the best of both worlds:
- You get to eat whatever you want—for five days a week, no food is off-limits.
- You only restrict calories for two days—these fasting days limit intake to about 25% of daily needs (roughly 500-650 calories).
- It’s sustainable—unlike traditional diets that require constant restriction, fasting is temporary, making it easier to stick with long term.
And the science behind it? Promising.
Studies on mice have shown that fasting can extend lifespan, reduce inflammation, and improve metabolic function.
But until now, little research had been done on how it affects healthy young adults.
So, scientists decided to put it to the test.
What Researchers Discovered About Fasting
A team from Harvard Medical School and the University of Florida recruited 24 healthy participants (ages 19-30) to follow a controlled fasting schedule for six weeks.
- For three weeks: Participants alternated between low-calorie days (650 calories) and high-calorie days (4,550 calories for men, slightly less for women).
Then, after a two-week break: They repeated the fasting cycle while also taking antioxidant supplements (vitamins C and E). - What they measured: Researchers tracked weight, blood pressure, heart rate, glucose levels, cholesterol, inflammation markers, and specific “longevity” genes known as SIRT1 and SIRT3.
And that’s where things got fascinating.
Fasting Activated the “Longevity Switch”—But Only Without Antioxidants
During the fasting phase, researchers found something remarkable:
- Fasting activated genes (SIRT1 and SIRT3) linked to cell repair, longevity, and metabolic health.
- It lowered insulin levels, suggesting a potential anti-diabetic effect.
- It triggered mild oxidative stress, which seems to train cells to become more resilient.
In other words, fasting made cells stronger, more efficient, and better at fighting damage.
But then, they introduced antioxidant supplements—and everything changed.
- The benefits disappeared.
- The increase in SIRT1 and SIRT3 stopped.
- The drop in insulin levels reversed.
Why?
Because oxidative stress is actually a good thing—in small doses.
When we fast, the body experiences mild stress from free radicals—unstable molecules that can cause cell damage.
But in response, cells activate protective pathways (like the SIRT genes) to defend and repair themselves.
By taking antioxidants, the body doesn’t get the signal to switch on these protective mechanisms.
“You need some pain, some inflammation, some oxidative stress for some regeneration or repair,” said researcher Christiaan Leeuwenburgh.
Essentially, the antioxidants shielded the body from the stress signals that make fasting beneficial in the first place.
This contradicts a long-standing belief that taking antioxidants is always beneficial.
It turns out, when combined with fasting, they might actually interfere with the body’s natural repair process.
Challenging What We Think We Know About “Health”
For decades, antioxidants have been marketed as essential for preventing aging and disease.
Vitamin C. Vitamin E. Green tea extract. We’ve been told they’re the key to fighting free radicals and staying youthful.
But this study suggests a paradox—too many antioxidants could actually weaken the body’s natural defense system rather than strengthen it.
This isn’t the first time researchers have questioned antioxidant supplements:
- A 2007 study found that supplementing with vitamins C and E blunted the benefits of exercise.
- Another study in 2011 suggested that antioxidants could reduce the lifespan of certain animals rather than extend it.
- Clinical trials on cancer patients have raised concerns that some antioxidant supplements might actually accelerate tumor growth.
So while foods rich in natural antioxidants (like berries, nuts, and leafy greens) are still beneficial, popping high-dose antioxidant pills might not be the “health hack” we once thought.
Intermittent Fasting Is About More Than Just Weight Loss
Perhaps the most surprising finding of the study was this:
- The positive effects of fasting happened even without weight loss.
Many people assume that fasting works only because of calorie restriction. But this research suggests that fasting triggers unique biological responses—separate from just eating fewer calories.
This could have huge implications for diabetes prevention, aging, and even disease management.
For example:
- Lower insulin levels → Could help prevent type 2 diabetes.
- Cellular repair activation → May play a role in slowing aging and disease.
- Increased stress resilience → Might improve immune function and overall health.
Fasting isn’t just about cutting calories—it’s about training your body to adapt and become stronger.
So, Should You Stop Taking Antioxidants?
Before you toss out your vitamin bottles, it’s important to remember:
- This study was small (24 participants), and more research is needed.
- Not all antioxidants are bad—natural sources from food are still beneficial.
- The key takeaway isn’t to avoid antioxidants entirely—but to be mindful of when and how you use them.
If you’re practicing intermittent fasting, it may be worth avoiding high-dose antioxidant supplements on fasting days so your body can fully activate its natural defense mechanisms.
And if you’re someone who relies on supplements, consider getting your antioxidants from whole foods instead—where they exist alongside other beneficial compounds that help balance their effects.
What This Means for the Future of Health and Longevity
This study challenges conventional wisdom about antioxidants and intermittent fasting, suggesting that sometimes, a little stress is exactly what our bodies need.
Rather than shielding ourselves from every possible source of oxidative stress, it may be more beneficial to harness it in controlled doses—through fasting, exercise, and other natural stressors.
So, the next time you’re considering that vitamin C pill, ask yourself:
Are you really helping your body?
Or are you getting in the way of its ability to heal itself?
The science of longevity is evolving, and this study is just the beginning.
One thing is clear: our bodies are more resilient than we think—if we let them be.
