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Lose a Pound of Fat in ONE Day: Century Fat Burner

Legal disclaimer: Since we are not doctors, never follow anything based on health-related or training topics on this or related sites without first consulting with your doctor or other trusted health professional.

A pound of body fat nominally equates to 3500 calories (kilocalories).

Be sure to read Fat Loss vs Weight Loss and Muscle Loss.

It is possible to lose a pound of body fat in one day (or thereabouts).

Riding a century or double century necessarily forces an effort level which is primarily aerobic (utilizing oxygen), because the effort is ~6 to ~16 hours. It is impossible for the body to do otherwise for a 4000-8000 calorie ride (century or double century).

Aerobic means that body fat is being utilized as the primary energy source.

Where the energy comes from during a ride

During a long moderate (primarily aerobic) effort, the body will (must) take the majority of its energy needs from fat. Energy sources include:

  • Body fat (essentially limitless energy even for very long events);
  • Glycogen stores in the muscles, liver, etc (exhausted in ~2 hours);
  • Glycogen consumed while riding (or things that break down into it);
  • Catabolic muscle loss (body “eats” its own muscles, consider Perpetuem).

It is impossible for the body to do otherwise for a 4000-8000 calorie ride (century or double century). There is no other energy source which can supply that number of calories (not possible to take in, digest, utilize anywhere near that amount while riding, especially if dehydration comes on).

Here then is the secret: a very long ride burns primarily body fat. The more moderate the pace, the more body fat is utilized for energy.

What happens after the ride depends on when you eat, what you eat, how much you eat, etc. By eating right, that body fat has been disappeared; whethere it is replaced depends on subsequent dietary behaviors. So the approach is relatively simple:

  • Do one very long ride per week; this will burn off mostly fat.
  • Eat to “caloric parity” or a slight deficit the other days (and eat enough to recover from the long effort!).
  • Repeat.

When done, always eat to satiety in reasonable portions with dietary balance utilizing caloric pacing (not one monster meal), and not skimping on fats or protein and nutrient-rich foods, and not loading up on sugars and equivalents. You cannot eat enough to replace the calories burned for such a long effort (barring drinking oil or eating a lot of very fatty food, obviously a poor nutritional idea for recovery alone).

What’s the catch? Fitness must have reached a level that allows completioin of a very long ride*. That can be achieved by almost anyone by steadily exercising for a few months (more if obese or very badly out of condition), which will itself burn off fat.

When body fat drops below ~8% (percentage varies by individual), further losses will become very difficult. Moreover, the risk of the body metabolizing muscle and favoring fat stores increases (survival mechanism). The more body fat to begin with, the easier it is to reduce it (at first); the leaner one gets, the more the body will take countermeasures to protect The Idiot Intent on Starving to Death. But it’s getting from that 20% or 15% or 12% body fat level down to 8% that the above approach can be helpful with.

By graphing weight daily, and utilizing “lower highs and lower lows”, it is possible to see discontinuities in body mass that result in a long effort of a single day—(weight for a few days after the long effort may be 'strange', for various reasons). Confirming hard proof of this fact in a series of DEXA scans over time.

* Very Long Ride = “why the hell was I stupid enough to start this?”, somewhere around 125 miles for a double century and 80 miles for a century.


Carbohydrates cannot be skipped for a long effort! Depending on effort level and body weight, ingest ~150-220 calories per hour (~100 calories every 30 minutes) of a maltodextrin gel like Hammer Gel (you need carbohydrates even if the primary energy source is fat). More than 300 calories per hour is generally non-productive, especially when dehydrated. Do not eat regular food unless you want to feel crummy.

In the example below, the SRM power meter recorded a 4650 kilojoule effort, or about 4450 kilocalories (calories). Let‘s analyze the “caloric burn”, keeping in mind that many factors influence the proportions:

  • 1100 calories of Hammer gel and similar were consumed during the effort.
  • Body stores of glycogen were likely low this day due to previous heavy training. Figure 900 calories of stored glycogen.
  • Figure energy from protein (catabolic losses from muscles) of about 500 calories.
  • Metabolic needs post-ride are ignored here (but quite significant).

In total, a rough estimate for this effort is that ~2500 calories come from glycogen and protein. The other energy must have come from 2450 calories of body fat. Or roughly 50% from fat.

The exact figures do not matter given significant variances by individual and effort level and so on, but a key point remains: somewhere around 7/10 of a pound of body fat had to be “burned” during this ride (2450/3500). A double century (slower pace) would thus burn ~1.5 pounds of body fat—gone in one day. Post-ride, body fat stores are likely to be called upon also, even with appropriate eating.

Stats: 100 miles in 6:07 riding time @ 216W @ 128 bpm, 68°F, 8140’ ascent
[~100.4 miles, taking into account tire size adjustment]
RED is heart rate, GREEN is power (watts). Click each graph for larger version.

Extensive endurance workout of 6+ hours burning 4650 kilojoules
Data from the SRM power meter (accurate to 1%).
Food eaten the day of a 4650 kilojoule century
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