The Fasting Cure: A Century-Old Diet Trend Meets Modern Science

In 1911, Upton Sinclair published The Fasting Cure, a provocative endorsement of fasting as a remedy for nearly every ailment—from fatigue and indigestion to chronic disease. But over a century later, how do his claims hold up against modern science?

What The Fasting Cure Got Right

1. Fasting Can Improve Metabolic Health

Sinclair’s assertion: Fasting clears the body of toxins and gives organs a rest.

Modern support: Intermittent fasting (IF) and time-restricted eating (TRE) improve insulin sensitivity, blood pressure, and cholesterol levels. A 2020 review in the New England Journal of Medicine found IF may reduce inflammation and promote cellular repair processes like autophagy—the body’s way of cleaning out damaged cells.

2. Overeating Is a Modern Problem

Modern support: Chronic overeating contributes to obesity, type 2 diabetes, and non-alcoholic fatty liver disease. Sinclair’s core message—less is more—is echoed today in caloric restriction and fasting-mimicking strategies.

What Has Changed (and Why It Matters)

1. Fasting as a Cure-All? Not Quite.

Modern correction: Fasting is not a panacea. While it may improve risk factors, it cannot cure diseases like tuberculosis or cancer. In fact, fasting without supervision can be dangerous—especially for people with diabetes, low blood pressure, or eating disorders.

What’s valid today: Structured fasts may complement treatments under medical supervision—but not replace them.

2. The “Water-Only” Fast Is Risky

Modern update: Extended water-only fasts can cause electrolyte imbalances, muscle loss, and even organ failure. Safer, modern fasting protocols include:

  • Time-restricted eating (e.g., 16:8): Eating within an 8-hour window
  • 5:2 fasting: Two low-calorie days per week
  • Fasting-mimicking diets: Low-calorie, plant-based 5-day programs

What Modern Research Adds

1. Autophagy and Longevity

Studies show fasting can trigger autophagy—a cellular clean-up process—and may promote longevity through pathways linked to metabolism and stress resistance.

2. Gut Health and Circadian Rhythms

Modern studies show fasting improves gut microbiome diversity and aligns digestion with circadian rhythms, which helps with immunity, digestion, and even sleep quality.

3. Psychological Benefits

Sinclair noted improved clarity during fasting. Today, some studies back this, showing improved mental focus and mood during short-term fasts.

What Conditions Can Fasting Help?

While not a cure, fasting can support treatment for several chronic conditions:

  • Type 2 Diabetes: Reduces insulin levels and improves insulin sensitivity
  • Obesity: Promotes fat burning and appetite regulation
  • High Blood Pressure: Often lowered through weight loss and improved vascular function
  • Fatty Liver Disease: Reduces liver fat through metabolic switching
  • Inflammatory conditions: Some fasting patterns may reduce systemic inflammation
  • Early cognitive decline: May protect brain cells through ketone production and reduced oxidative stress

Is Fasting Right for Me?

Fasting isn’t a one-size-fits-all solution. It may be right for you if you:

  • Struggle with weight management
  • Have prediabetes or insulin resistance
  • Experience energy crashes after meals
  • Are looking for ways to reduce inflammation

But consult your doctor first if you:

  • Are pregnant or breastfeeding
  • Have diabetes or take medications
  • Have a history of eating disorders
  • Are underweight or have adrenal/hormonal imbalances

Book Review: The Complete Guide to Fasting by Dr. Jason Fung

Summary: Dr. Jason Fung’s book is a go-to resource for anyone curious about fasting. Written in a clear, non-technical style, it covers intermittent fasting, alternate-day fasting, and extended fasts. It includes case studies, protocols, and common mistakes to avoid.

What makes it great:

  • Explains the science in simple terms
  • Includes real-life success stories and tips
  • Includes recipes and plans for various fasting types

Ideal for: Beginners, people with type 2 diabetes, and anyone interested in sustainable weight loss or reversing metabolic syndrome.

Get The Complete Guide to Fasting Book on Amazon!

Frequently Asked Questions (FAQs)

1. Does fasting mean starving?

No. Fasting is a voluntary abstention from food for health or spiritual reasons, while starvation is an involuntary lack of access to food. Fasting can be planned, controlled, and stopped at any time—starvation is dangerous and unintentional.

2. Will fasting make me lose muscle?

Not in the short term. Studies show that during intermittent fasting or short-term fasts (24-48 hours), the body increases growth hormone and uses fat for fuel first. Muscle breakdown only occurs in extended fasting (72+ hours) without adequate nutrition.

3. Can I fast if I work out?

Yes, you can. Many people do resistance training or cardio while fasting. In fact, training in a fasted state may improve fat burning. Just stay hydrated and listen to your body. Break your fast with a nutritious, protein-rich meal.

4. Is breakfast the most important meal of the day?

Not for everyone. The "breakfast myth" came from cereal marketing. What matters more is your total food intake and timing. Some people perform better with a delayed eating window (e.g., first meal at noon).

5. Does fasting slow down my metabolism?

No—short-term fasts can actually increase it. Fasting triggers norepinephrine, which can slightly raise resting energy expenditure. Prolonged calorie restriction over many weeks (not fasting) is what causes metabolic slowdown.

6. Will I be tired or weak while fasting?

Initially, maybe—but it usually improves. The first few fasts can feel sluggish, especially if you're used to frequent meals. But many people report more energy and mental clarity after adapting to a fasting routine.

7. Can I drink coffee or tea while fasting?

Yes, absolutely. Black coffee and unsweetened tea are fasting-friendly. They contain no calories and may even enhance the effects of fasting by supporting alertness and suppressing appetite.

8. Is fasting dangerous for women?

It depends. Some women thrive with fasting, while others may experience hormonal imbalances if they fast aggressively. A gentler approach (e.g., 12-14 hour fasts or non-daily fasting) is often better suited for women, especially during childbearing years.

9. Do I need supplements while fasting?

Not usually for short fasts. But on fasts longer than 24-48 hours, you may benefit from electrolytes like sodium, potassium, and magnesium. Multivitamins can also help if fasting multiple days in a row.

10. Can I fast if I’m not trying to lose weight?

Yes. Fasting offers benefits beyond fat loss—like improved insulin sensitivity, reduced inflammation, and better cognitive function. Many people fast for metabolic health, not just weight management.

Final Verdict: A Mixed Legacy

The Fasting Cure was radical in its time—and some of Sinclair’s core beliefs now have scientific merit. But much of his advice overshoots the evidence and ignores the risks of extreme fasting. Modern science supports fasting when it’s done safely, within boundaries, and alongside a balanced diet.

Takeaway: If You’re Interested in Fasting...

  • Start with time-restricted eating (e.g., 12pm–8pm)
  • Consult a doctor if you have any chronic conditions
  • Avoid water-only fasts longer than 24 hours unless supervised
  • Eat whole, minimally processed foods during eating windows
  • View fasting as a tool—not a cure-all

References

  1. de Cabo, R., & Mattson, M. P. (2020). Effects of intermittent fasting on health, aging, and disease. New England Journal of Medicine.
  2. Longo, V. D., & Panda, S. (2016). Fasting, circadian rhythms, and time-restricted feeding in healthy lifespan. Cell Metabolism.
  3. Zarrinpar, A., et al. (2014). Time-restricted feeding alters the gut microbiota. Cell Metabolism.
  4. Anton, S. D., et al. (2018). Flipping the metabolic switch: Understanding and applying health benefits of fasting. Obesity.