Why Very Overweight People Often Find Fasting Easier
It seems counterintuitive. You might expect that someone carrying 50 or 100 extra pounds would struggle most with going without food. Yet Upton Sinclair's 1911 book The Fasting Cure documented something that surprised him and his contemporaries: the more overweight a person was, the more readily they often adapted to fasting — and in some cases, the more striking their results.
This observation, made more than a century ago, turns out to align surprisingly well with what modern science now understands about fat storage, fuel metabolism, and hunger signalling.
A Historical Pattern Sinclair Noticed
In The Fasting Cure, Sinclair collected reports from 277 fasting episodes across 109 individuals. Among his observations and correspondence from readers was a recurring theme: people who were significantly overweight often described fasting as easier than they expected, and their recoveries tended to be dramatic.
Sinclair wrote that after a complete fast, "the body will come to its ideal weight. People who are very stout will not regain their weight; while people who are under weight may gain a pound or more a day for a month." He was describing what he saw as the body's natural regulatory intelligence — using available stored fuel first.
This wasn't just anecdote. The cases he collected included men who had weighed 220 pounds with legs "like sacks of water," who fasted for 7 days and then followed a light diet, returning to farm work — chopping wood, pitching hay — within weeks. Another was a woman who "barely crawled on two sticks" and fasted 10 days, then 8 more days, eventually described as having "superabundant and radiant health."
Sinclair framed all of this in the language of his era: fermentation, toxins, clogged vessels. But the core observation was real: the body of an overweight person has a significant and accessible fuel reserve.
Why It Makes Physiological Sense
Modern metabolism explains what Sinclair observed in anecdotal terms. Adipose tissue — stored body fat — exists precisely as an energy reserve. When carbohydrate stores run low (usually within 12–18 hours of fasting, depending on the individual), the body begins to draw on fat stores for fuel.
For someone with substantial fat reserves, this transition provides a longer runway. The body has more raw material to draw on before it turns to other fuel sources. Hunger in early fasting is largely driven by drops in blood glucose and the hormonal patterns associated with regular mealtimes — not by a true lack of available energy. A person with 30 extra kilograms of fat has extraordinary energy reserves; their cells are never actually starving.
This is the key distinction between fasting and starvation. Starvation occurs when the body exhausts its reserves and begins breaking down essential tissue. Fasting, even extended fasting, operates through the fat-burning pathway — and for someone significantly overweight, that pathway is wide open.
The First Few Kilos and Water Weight
There is an additional factor that Sinclair's era didn't fully understand but modern fasting practitioners recognize immediately: glycogen depletion and water loss.
When a person begins fasting (or dramatically reduces carbohydrate intake), the liver depletes its glycogen stores. Each gram of glycogen holds approximately 3–4 grams of water. When this glycogen burns off, several kilograms of water weight releases rapidly — often 2–4 kilograms in the first few days.
For someone who is significantly overweight, this initial rapid loss — visible on the scale within days — provides powerful early motivation. While it is not fat loss in the true sense, it signals that the body has shifted into fasting mode, and it makes the early days feel productive rather than pointless.
Sinclair noticed this in his own experience: he lost 15 pounds in the first 4 days of his 12-day fast, then far less in the following 8 days. He interpreted this as a sign of "extremely poor tissue state." Today we recognize it largely as glycogen and water releasing.
Hunger Behaves Differently in the Overweight
Hunger is partly hormonal. Ghrelin, often called the "hunger hormone," is known to fluctuate with meal timing and habitual eating patterns. Among people with obesity, ghrelin signalling is often disrupted — sometimes resulting in more complex and less sharp hunger signals compared to lean individuals.
Sinclair also noted — and this holds up — that once genuine hunger passes (typically after the second or third day of a complete fast), the body adapts to running on stored fuel. For overweight individuals who have larger fat reserves available, this adaptation can be smoother. The body has plenty of fuel; it simply needs to switch which tanks it's drawing from.
The Important Caveat: Fat Loss Is Not Always Linear
Sinclair's observation that overweight fasters often experience dramatic early results is accurate, but it comes with an important nuance — one he also noted.
The first weight lost is the easiest. As fat stores reduce and the body approaches a healthier weight range, the rate of loss slows. The last 10–15 kilograms are consistently harder than the first. The body defends its remaining fat more aggressively, and this is true whether you're fasting or doing any other form of caloric restriction.
Belly fat in particular tends to be the most resistant. As the author of Intermittent Fasting in Practice explains, the body burns fat from other areas first — face, limbs, general trunk — before attacking the deep visceral fat stored around the abdomen. Consistency over months, not weeks, is what ultimately shifts that.
What Sinclair Got Right About the Ideal Weight Mechanism
Sinclair wrote that fasting "brings you to your ideal weight" — a phrase that sounds mystical but has a practical mechanism behind it.
When the body is no longer receiving excess food, it stops storing. It begins to utilize what it has. A body running on fat stores gradually draws those stores down. It doesn't continue shrinking indefinitely — once it reaches a weight at which the caloric intake from food at the eating window matches actual needs, weight stabilizes.
Sinclair's observation that very overweight fasters "do not regain their weight" (after a proper fast and clean diet post-fast) reflects what happens when people make dietary improvements alongside fasting — reducing the foods that drove the excess accumulation in the first place.
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Frequently Asked Questions
Is it really easier for overweight people to fast?
In several specific ways, yes. The main reason is available fuel. Someone with significant fat reserves has more stored energy for the body to draw on when dietary intake stops. This means the brain and muscles are not actually deprived of fuel — they're simply running on a different fuel source. The hunger and adaptation period can still be challenging, but the body has more to work with.
Do very overweight people lose weight faster with intermittent fasting?
Early results are often more dramatic, particularly in the first few weeks. Much of this is water and glycogen loss as the body depletes stored carbohydrates. Actual fat loss rates vary, but people with more to lose tend to lose weight faster in absolute terms than those closer to their goal weight.
Can fasting be dangerous for someone who is significantly overweight?
As with any significant dietary change, a consultation with a healthcare provider is appropriate before starting. Certain conditions common with obesity — type 2 diabetes on medication, hypertension treated with diuretics, cardiovascular disease — require medical oversight when fasting. Most otherwise healthy overweight individuals can begin with shorter fasting windows (12–14 hours) safely.
What did Sinclair's cases show for very overweight fasters?
Several of Sinclair's most dramatic cases involved people who were significantly overweight. One man with dropsy (severe fluid retention) weighing 220 pounds fasted 7 days, then followed a light diet, and returned to hard farm labour. His case — and others like it — suggested that the body has a remarkable capacity to draw on accumulated reserves when given the opportunity.
Does the body ever run out of fat to burn?
During intermittent fasting as most people practice it (daily windows of 16–18 hours), the body does not run out of fat during the fasting period. It burns as much as it can access given the window length. Over months of consistent practice, fat stores reduce gradually — which is when longer windows or more careful food choices in the eating window may be needed to continue progress.
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This article draws on historical research from 1911 and is for informational purposes only — not medical advice. Always consult a qualified healthcare professional before making any dietary changes.
Sinclair, U. (1911). The Fasting Cure. Mitchell Kennerley.