I've been getting this question a lot lately, and honestly, it's making me realize how much I glossed over one of the most important aspects of my FMD experiments: what exactly happens when you try to maintain your coffee habit while your body is running on 700 calories a day.

Valid concern. When I was researching my first FMD attempt, I spent way too much time diving into the minutiae of glycerol supplementation and vegetable ratios, but somehow glossed over the coffee situation. Which is bizarre, considering I'm someone who considers her morning espresso a non-negotiable life requirement.

Here's what I discovered about coffee during FMD—and why the answer isn't as straightforward as I initially thought.

The Official Word (And Why It Matters)

According to Dr. Valter Longo's research, black coffee is generally acceptable during the fasting mimicking diet. The key word here is "black"—no cream, no sugar, no fancy oat milk additions that would bump up your calorie or protein counts.

The reasoning makes sense from a metabolic perspective. Plain coffee contains virtually no calories and doesn't significantly impact the cellular processes that FMD is designed to trigger. Your body stays in that beneficial fasting state while you get to maintain some semblance of morning normalcy.

But here's where it gets interesting: not all coffee experiences during FMD are created equal.

My First-Round Coffee Reality Check

During my initial five-day experiment, I assumed coffee would be my saving grace—the one familiar comfort that would make the whole experience bearable. I figured I'd just drink my usual amount and everything would be fine.

That assumption lasted exactly one day.

On day two, my regular coffee routine hit me like a freight train. That familiar caffeine boost felt more like caffeine jitters, and by midday I was dealing with what felt like the world's most unfair crash. My heart was racing, my hands were slightly shaky, and I felt like I'd had way more coffee than my usual two cups.

Turns out, when your body is running on significantly fewer calories, caffeine affects you differently. Your normal tolerance basically goes out the window.

The Timing Strategy That Actually Works

Here's what I learned through trial and error: when you drink coffee during FMD matters almost as much as what you drink.

Morning coffee: Generally fine, but start with half your usual amount. Your empty stomach processes caffeine much faster than usual, so that regular strength hits harder and faster.

Afternoon coffee: Proceed with caution. What used to be a perfectly normal 2 PM pick-me-up can easily become a recipe for evening anxiety when your system is already running on stress hormones from the calorie restriction.

Evening coffee: Just don't. Trust me on this one.

For my second round, I stuck to one cup in the morning and occasionally a very weak second cup before noon. This gave me the psychological comfort and mild energy boost without the jittery aftermath.

Quality Over Quantity Becomes Crucial

One unexpected benefit of drinking less coffee during FMD: I became way more intentional about the coffee I was drinking. When you're only having one cup, you want it to be really good.

I started making my morning coffee more of a ritual—better beans, proper brewing method, actually sitting down to drink it instead of rushing around. This mindful approach ended up being more satisfying than my usual multi-cup routine.

There's something about savoring a single, well-made cup that feels more aligned with the intentional nature of FMD anyway.

The Withdrawal Factor Nobody Talks About

Here's something I wish someone had warned me about: if you're a heavy coffee drinker, reducing your intake during FMD can add caffeine withdrawal symptoms on top of the normal fasting side effects.

I learned this the hard way during round one. By day three, I was dealing with a headache that I initially attributed to the fasting, but was probably at least partially caffeine withdrawal. The combination of reduced calories and reduced caffeine created a perfect storm of feeling terrible.

For subsequent rounds, I started tapering my coffee intake a few days before beginning FMD. Not dramatic—just dropping from three cups to two, then two to one. This small adjustment made the transition much smoother.

The Decaf Experiment That Surprised Me

During my third FMD cycle, I decided to test something: what if I switched to decaf after my morning cup?

I expected this to be torture, but it was actually pretty enlightening. The ritual of having something warm to drink throughout the day was almost as important as the caffeine itself. Decaf coffee gave me the psychological comfort without any additional metabolic stress.

This approach worked especially well on days 4 and 5, when I wanted the comfort of my usual routine but my body was most sensitive to stimulants.

What About Coffee Alternatives?

For those times when coffee felt like too much, I experimented with other warm beverages that fit within FMD guidelines:

Herbal teas: Obviously fine, and some like ginger or peppermint actually helped with any digestive discomfort from the diet.

Green tea: Lower caffeine than coffee, but still enough to provide a gentle energy boost without the intensity.

Bone broth: Technically not coffee-related, but having something warm and savory was sometimes more appealing than another cup of anything caffeinated.

The key was having options so I wasn't white-knuckling it through moments when I really wanted something comforting to drink.

The Mental Game of Coffee During FMD

One thing I didn't anticipate was how much the coffee question would become about psychology rather than physiology. My morning coffee routine was deeply tied to feeling "normal" and in control.

When that routine gets disrupted—even if you're still drinking coffee, just less of it—it can feel destabilizing in ways that have nothing to do with caffeine addiction. It's about maintaining some element of your regular life while everything else feels different.

Understanding this helped me be more intentional about other small comforts I could maintain during FMD. Maybe it wasn't about the coffee itself, but about having predictable moments of pleasure during an otherwise restrictive period.

The Bigger Picture on Stimulants

Coffee was my gateway to thinking more broadly about how stimulants interact with fasting periods. When your body is already under the stress of calorie restriction, adding additional stressors (like too much caffeine) can push you past your comfort zone into genuinely unpleasant territory.

This applies to other things too: intense workouts, alcohol, even staying up late. FMD taught me to be more aware of how these factors compound rather than exist in isolation.

What I'd Tell Someone Starting Their First FMD

If you're a coffee drinker planning your first fasting mimicking diet, here's my practical advice:

Start reducing your intake a few days before you begin. Aim for about half your normal amount during FMD. Make your morning cup count—better quality, more mindful consumption. Have backup options for when coffee feels like too much.

Most importantly, don't make coffee another thing to stress about during an already challenging process. The goal is supporting your body through the fast, not creating additional rules to follow perfectly.

The research supports moderate coffee consumption during FMD, your body will adapt to the changes, and you'll probably discover some interesting things about your caffeine habits in the process.

The Long-Term Coffee Revelation

Perhaps the most unexpected outcome of adjusting my coffee intake during FMD: I never went back to my pre-fast consumption levels. Not because I was restricting myself, but because I genuinely preferred drinking less, higher-quality coffee.

That mindful approach I developed during those five days carried over into regular life. I started tasting my coffee instead of just consuming it for caffeine delivery. I began noticing how different amounts affected my energy and mood throughout the day.

FMD accidentally taught me something valuable about my relationship with coffee that had nothing to do with fasting and everything to do with being more intentional about daily habits.

The Bottom Line

Coffee during FMD is generally fine, but it's worth approaching thoughtfully rather than automatically. Your tolerance will be different, your needs might change day by day, and there's an opportunity to use this as a chance to reset your relationship with caffeine.

The goal isn't to make FMD harder by eliminating something you enjoy, but to support the process by being smart about how stimulants affect your body during a period of metabolic change.

Have you experimented with coffee during extended fasting periods? I'm curious about others' experiences with caffeine tolerance during FMD—did you notice similar changes, or was your experience completely different?

Quick disclaimer because safety and science matter: This is my personal experience with coffee during fasting mimicking diets, not medical advice. Always consult healthcare providers about dietary changes, especially during fasting periods. ProLon® is Dr. Valter Longo's research-backed program—I'm just sharing what worked for my DIY approach.