I have been following a loose 2000-2400 kcal/day schedule of high protein, low-fat with hardly any cheat days for about a year and a half. The fat loss was pretty slow, but I wasn't in a real hurry. Over that period, I dropped about 40 pounds (245->205).
Over that time, I never felt like I was hungry at all. I think that I am pretty good being "hungry" in that I can more or less function fine, train fine and don't snap at co-workers or family. Lately, I have dropped down to about 1800-2200 kcal/day and still feel fine, but I am seriously considering dropping down to 1500 kcals/day for a few weeks to see how I feel. That would probably be about 1300 kcal/day below my expenditure, which is (check my math) about 1/3 pound fat/day or 2.25 pounds per week.
You might want to read up on the Minnesota Starvation Experiment from World War II in which they starved participants on 1500 calories and documented the effects before you engage in such methods.
Goals and methods
The primary objective of the Minnesota Starvation Experiment was to study in detail the physical and psychological effects of prolonged, famine-like semi-starvation on healthy men, as well as their subsequent rehabilitation from this condition. To achieve these goals, the 12-month study was divided into four distinct phases:
Control Period (12 weeks): This was a standardization period when the subjects received a controlled diet of approximately 3,200 calories of food each day. The diet of the subjects who were close to their “ideal” weight was adjusted so as to maintain caloric balance, while the diets of the underweight and overweight individuals was adjusted so as to bring them close to their ideal weight. On average, the group ended up slightly below their “ideal” weight.[2]:74 In addition, the clinical staff of the Laboratory of Physiological Hygiene routinely conducted a series of anthropometric, physiological and psychological tests designed to characterize the physical and mental health of each participant under normal conditions.
Semi-Starvation Period (24 weeks): During the 6-month semi-starvation period, each subject’s dietary intake was cut to approximately 1,560 calories per day. Their meals were composed of foods that were expected to typify the diets of people in Europe during the latter stages of the war: potatoes, rutabagas, turnips, bread and macaroni.
Restricted Rehabilitation Period (12 weeks): The participants were divided into four groups of eight men; each group received a strictly-controlled rehabilitation diet, consisting of one of four different caloric energy levels. In each energy-level group, the men were further subdivided into subgroups receiving differing protein and vitamin supplements regimes. In this manner, the clinical staff examined various energy, protein and vitamin strategies for re-nourishing the subjects from the conditions of famine induced during the semi-starvation period.
Unrestricted Rehabilitation Period (8 weeks): For the final rehabilitation period, caloric intake and food content was unrestricted but carefully recorded and monitored.
During the starvation period, the subjects received two meals per day designed to induce the same level of nutritional stress for each participant. Since each subject had distinct metabolic characteristics, the diet of each man was adjusted throughout the starvation period to produce roughly a 25% total weight loss over the 24-week period.
The researchers tracked each subject's weight as a function of time elapsed since the beginning of the starvation period. For each subject, the weight versus time plot was expected—as well as enforced—to form a particular curve, the prediction weight-loss curve, whose characteristics were decided prior to the commencement of the experiment. The postulated curves turned out to be quite predictive for most subjects. If a subject did veer off his curve in any given week, his caloric intake for the next week would be adjusted, by varying the amount of bread and potatoes, to bring him back to the curve; however, the required adjustments were usually minor.[2]:75 The shapes of the curves were chosen “based on the concept that the rate of weight loss would progressively decrease and reach a relative plateau” at the final weight.[2]:74
For each subject, the weight vs. time curve was taken to be quadratic in time (in fact, an upward-opening parabola) with the minimum located at 24 weeks, at which point the weight is supposed to be equal to the final target body weight (the minimum is where the curve has zero slope; this corresponds to the “plateau” mentioned above). Mathematically, this means that the curve for each subject was given by
W(t)=W_{f}+K\, (24-t)^{2},
where t is the time (measured in weeks) elapsed since the beginning of the starvation period, W(t) is the subject’s weight at time t, and W_{f} is the final weight that the subject was supposed to reach at the end of the 24-week period. The constant K is determined by the requirement that W(t=0) be the initial weight W_{i}, i.e. by solving
W_{i}=W_{f}+K\, (24-0)^{2}
for K; this gives
K=\frac{W_{i}-W_{f}}{24^{2}}.
The authors expressed this in terms of the percent total weight loss P,
P=100 \times \frac{W_{i}-W_{f}}{W_{i}}
(which, as stated above, was supposed to be about 25% for all subjects), obtaining
K=\frac{P}{100 \times 24^{2}}\,W_{i}.
Throughout the duration of the study each man was assigned specific work tasks, was expected to walk 22 miles each week and required to keep a personal diary.[4] An extensive battery of tests was periodically administered, including the collection of metabolic and physical measurements; X-ray examinations; treadmill performance; and intelligence and psychological evaluation.
ResultsThe full report of results from the Minnesota Starvation Experiment was published in 1950 in a two-volume, 1,385 page text entitled The Biology of Human Starvation (University of Minnesota Press). The 50-chapter work contains an extensive analysis of the physiological and psychological data collected during the study, and a comprehensive literature review.
Among the conclusions from the study was the confirmation that prolonged semi-starvation produces significant increases in depression, hysteria and hypochondriasis as measured using the Minnesota Multiphasic Personality Inventory. Indeed, most of the subjects experienced periods of severe emotional distress and depression.[1]:161 There were extreme reactions to the psychological effects during the experiment including self-mutilation (one subject amputated three fingers of his hand with an axe, though the subject was unsure if he had done so intentionally or accidentally).[5] Participants exhibited a preoccupation with food, both during the starvation period and the rehabilitation phase. Sexual interest was drastically reduced, and the volunteers showed signs of social withdrawal and isolation.[1]:123-124 The participants reported a decline in concentration, comprehension and judgment capabilities, although the standardized tests administered showed no actual signs of diminished capacity. There were marked declines in physiological processes indicative of decreases in each subject’s basal metabolic rate (the energy required by the body in a state of rest), reflected in reduced body temperature, respiration and heart rate. Some of the subjects exhibited edema in their extremities, presumably due to decreased levels of plasma proteins given that the body's ability to construct key proteins like albumin is based on available energy sources.
