The Fasting Mimicking Diet (FMD), popularized by the ProLon program developed by Dr. Valter Longo at USC, is a 5-day plant-based regimen designed to trigger cellular rejuvenation and other health benefits associated with fasting, without a full-water fast. The number of calories per day on the fasting mimicking diet follows a specific, step-down schedule to signal the body to enter a fasted state. This precise, low-calorie approach is key to its mechanism, influencing nutrient-sensing pathways like IGF-1, PKA, and mTOR.
Daily Caloric and Macronutrient Targets
The FMD follows a structured approach to its caloric and macronutrient delivery. The goal is to provide just enough fuel to avoid triggering growth-related pathways, while still providing some energy and nutrients.
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Day 1: The Transition
- On the first day, the caloric intake is around 1,100 calories.
- This initial intake is significantly lower than a typical diet but is designed to ease the body into the fasting phase.
- The macronutrient breakdown is carefully set to initiate the metabolic shift. Approximately 10–11% of calories come from protein, 46–56% from unsaturated fats, and 34–43% from complex carbohydrates. This initial ratio is fat-dominant to help prepare the body for the ketosis that typically begins later in the fast.
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Days 2–5: Deepening the Fast
- For the remainder of the 5-day cycle, the daily caloric intake drops to a range of 700–800 calories. The ProLon version specifies 725 calories.
- This lower calorie level, combined with the specific macronutrient ratio, is intended to intensify the fasting effects, promoting processes like autophagy and ketogenesis.
- The macronutrient profile also shifts slightly during this phase, becoming more balanced between fats and carbs. Typically, the distribution is around 9% protein, 44–47% fat, and 44–47% carbohydrates. The carbohydrate increase comes from complex, fiber-rich sources.
Key Differences from Other Fasting Methods
The FMD is often compared to other popular fasting methods, but it's important to understand the distinctions. Unlike a full water fast, the FMD provides nourishment, which can make it more manageable for some individuals. It also differs from intermittent fasting, which typically focuses on time-restricted eating windows without specific calorie or macronutrient restrictions.
Comparison of Fasting Protocols
| Feature | Fasting Mimicking Diet (FMD) | Intermittent Fasting (e.g., 16:8) | Water Fasting |
|---|---|---|---|
| Duration | 5 consecutive days, repeated periodically (e.g., every 1-6 months) | Daily fasting windows (e.g., 16 hours fasting, 8 hours eating) | Varies, can be 24-72 hours or longer under medical supervision |
| Calorie Intake | Yes, specific low-calorie intake (approx. 1100 kcal Day 1, 725-800 kcal Days 2-5) | No strict calorie counting during eating window, though moderation is key | None, except for water |
| Food Type | Plant-based, with specific macronutrient ratios | No specific food restrictions | Water only |
| Goal | Mimic fasting effects while providing sustenance and nutrients | Restrict eating windows to reduce overall caloric intake | Maximize the fasting state to promote autophagy and other benefits |
Making the FMD Work: DIY vs. Pre-Packaged Kits
For those considering the FMD, there are two primary options: using a pre-packaged kit, such as ProLon, or attempting a DIY approach. The ProLon kit is scientifically formulated and tested, containing precise macro- and micronutrient combinations intended to maximize the desired cellular responses. It removes the guesswork and simplifies the process for users. However, it can be costly.
Alternatively, a DIY FMD can be created using plant-based whole foods, focusing on the specific calorie and macronutrient guidelines. This requires careful meal planning, tracking, and preparation to ensure the targets are met. Examples of FMD-approved foods include vegetable-based soups, nut bars, olives, and leafy greens. While a homemade version offers more flexibility and may be cheaper, it has not been clinically studied like the proprietary product, so its effectiveness in inducing the intended biological pathways cannot be guaranteed.
The Role of Macronutrients and Cellular Pathways
Beyond just calories, the specific ratio of macronutrients is crucial for the FMD's effects. The diet's composition—low protein, low carbohydrates, and high unsaturated fats—is designed to down-regulate specific nutrient-sensing pathways in the body. For instance, limiting protein reduces the activation of IGF-1 and mTOR, while controlling carbs manages PKA. This manipulation of pathways is what 'tricks' the body into a fasted state, triggering processes like cellular repair (autophagy) and fat burning (ketogenesis).
Conclusion
In conclusion, the fasting mimicking diet is a structured 5-day regimen involving a specific calorie breakdown: approximately 1,100 kcal on day one and 700-800 kcal on days two through five. The diet's effectiveness hinges on adhering to both the calorie counts and the plant-based, low-protein, high-fat macronutrient ratios, which are designed to induce the benefits of prolonged fasting while consuming a limited amount of food. Whether using a kit like ProLon or a careful DIY approach, individuals interested in the FMD should consult a healthcare provider to ensure it is safe and appropriate for their health needs. For more detailed information on the diet's scientific background, the work of Dr. Valter Longo provides extensive resources on the USC Longevity Institute website.
