Calorie Deficit Statistics: Fat Loss by the Numbers

The 3,500-kcal-per-pound rule grossly overestimates actual weight loss when checked against seven supervised weight-loss experiments

The authors compared predicted with measured loss in confinement studies and offer a validated dynamic model instead. A fixed 500 kcal daily deficit does not keep producing a pound a week.

Body weight responds slowly to a change in energy intake, with a half-time of about 1 year

Mathematical model of adult metabolism with a public web simulator. People with more body fat lose more for the same intake change and take longer to reach their new steady weight.

Keeping body weight 10% or more below its starting level reduced total daily energy expenditure by 6 ± 3 kcal per kg of fat-free mass in never-obese people and 8 ± 5 kcal in people with obesity

18 obese and 23 never-obese adults measured at usual weight and after losing 10-20%. Resting and non-resting expenditure each fell 3-4 kcal per kg of fat-free mass. For 60 kg of fat-free mass, 6-8 kcal per kg is 360-480 kcal a day.

The lower energy expenditure after a 10% weight loss persisted in people who had kept the weight off for more than a year

Seven matched trios studied on an identical liquid diet: one at usual weight, one recently reduced, one reduced for over a year. Expenditure was similarly low in both reduced groups.

More than 80% of people who lose weight return to their previous level of body fat

Review of 'adaptive thermogenesis': coordinated metabolic, behavioural, hormonal and nervous-system responses, largely driven by leptin, that defend body fat after a loss.

About 20% of people with overweight succeed at long-term weight loss, defined as losing at least 10% of body weight and keeping it off for at least a year

Review drawing on the National Weight Control Registry. After 2-5 years of successful maintenance, the chance of longer-term success rises sharply.

National Weight Control Registry members lost an average of 33 kg and kept it off for more than 5 years

They report about an hour a day of physical activity, a low-calorie and low-fat diet, regular breakfast, self-weighing and a consistent eating pattern across the week. Registry members are a self-selected group of successes.

Obese patients who said diets did not work for them underreported their food intake by 47% and overreported their physical activity by 51%

Measured in 10 'diet-resistant' patients from 224 consecutive obese patients. Their energy expenditure was within 5% of predicted, ruling out a slow metabolism.

Elite athletes losing 0.7% of body weight a week gained 2.1% lean body mass; those losing 1.4% a week gained none

24 athletes randomized, all strength training four times a week. Energy intake was cut by 19% in the slow group and 30% in the fast group, and both lost about 5.5% of body weight.

For contest preparation, a weekly weight loss of about 0.5-1% of body weight and 2.3-3.1 g of protein per kg of lean mass are recommended to keep muscle

Evidence review for natural bodybuilders; it also suggests 15-30% of calories from fat. Meal timing and frequency appear to have little effect on fat loss or lean-mass retention.

Alternating 2-week blocks of dieting with 2-week blocks at maintenance produced more weight loss (14.1 vs 9.1 kg) and fat loss (12.3 vs 8.0 kg) than continuous dieting

51 men with obesity were randomized; both groups ate 67% of maintenance during dieting blocks, so the intermittent plan took 30 weeks against 16. Fat-free mass loss was similar.

81% of diet-only groups and 39% of diet-plus-exercise groups lost at least 15% of their weight loss as fat-free mass

Systematic review of 52 studies in men and postmenopausal women aged 50 and over with a BMI above 25; the exercise was mainly aerobic.

Partial sleep deprivation increased energy intake by 385 kcal a day without changing energy expenditure

Meta-analysis of 11 studies with 172 participants. The extra intake came with more fat and less protein.

Digesting a mixed diet at energy balance costs 5-15% of daily energy expenditure

Review of diet-induced thermogenesis. The cost is highest for alcohol and protein, then carbohydrate, then fat, so higher-protein diets raise it.

Daily weighers lost 6.1 kg more over 6 months than participants who weighed less than daily

47 overweight adults in the intervention arm of a trial; those weighing less than daily still did so on 5.4 days a week. Daily weighers adopted more weight-control behaviours.

All 22 reviewed studies of self-monitoring diet, exercise or weight found it consistently associated with weight loss, though the evidence was weak

Systematic review of studies from 1993-2009. Samples were mostly white women, and adherence was usually self-reported.