An Objective Look at Intermittent Fasting, Part 1
Posted: Sun Aug 03, 2008 5:03 pm
By Alan Aragon and Ryan Zielonka
Introduction
The ancient practice of fasting seems to periodically find its way into modern fitness subcultures. Despite its purported physiological and psychological benefits, scientific data is far from unanimously supporting it. Are there any physiological advantages to increasing or decreasing meal frequency? What are the downsides to intermittent fasting? What are the health advantages shared by fasting, exercise, and caloric restriction? Are there detrimental effects of resistance training in a fasted state? Anecdotal data is fraught with suggestion-driven bias so we will focus on what has been demonstrated objectively in scientific research.
Meal frequency—hot dogma and cold facts
Since the health nut culture’s infancy, the decree has been that one must eat every 2–3 hours, thus minimizing muscle breakdown while keeping the metabolic engine revving. Tupperware containers and coolers in gyms and cars were (and still are) a common sight, perceived by the public to be a sign of diligence and discipline. However, the long held belief in a higher-is-better frequency has been examined with the lens of science, and some interesting data has surfaced.
Effects on health and thermogenesis
Research indicates that a haphazard meal frequency, not necessarily a lower frequency, negatively impacts thermogenesis, blood lipids and insulin sensitivity (1, 2). Contrary to popular belief, a high frequency has no thermodynamic advantage over a low frequency under calorie controlled conditions (as opposed to ad libitium or free living conditions) using 24-hour indirect calorimetry (3, 4). So much for the magic of stoking the metabolic furnace with an extreme grazing pattern. It bears mentioning that lower 24-hour insulin levels as well as lower fasting and total LDL-cholesterol levels have been observed with higher meal frequencies (5, 6). However, in discovering this, studies have used unrealistic protocols for the higher frequency treatments, comparing three meals to nine or 17 meals per day.
Effects on body composition
With little exception (7,
, the majority of controlled intervention trials show no improvement in body composition with a higher meal frequency, with treatments ranging from 1–9 meals per day (9–11, 15). Unfortunately, a scarcity of research examining meal frequency’s effect on body composition under conditions of exercise exists in the literature. To further confound the data, results from studies are mixed. The singular, full length published controlled trial showing a body composition benefit of higher meal frequency (six versus three) is limited by its poor study design. In the trial, boxers consumed a 1200 kcal liquid diet over a two-week period (8). The six-a-day group retained more lean mass than the three-a-day group.
In contrast to the boxer study, a recent abstract presented at the Twelfth Annual Congress of the European College of Sport Science reported the superiority of three meals a day to six meals a day for gaining lean mass during a 12-week period involving strength training (12). Too bad the three-a-day group also experienced a trend toward fat gain. This raises the possibility that the three-a-day group simply ate more calories overall. This wouldn’t be surprising, considering that comparative research shows an association of greater hunger with meal frequency reduction.
Effects on appetite
Studies indicating the disappearance or lack of hunger in dieters occur in either complete starvation or very low calorie regimes (800 kcal/day or less) (13, 14). Much of this data is irrelevant for most of you reading this. Furthermore, none of those studies systematically measured appetite throughout waking hours. Convenience issues aside, for the purposes of controlling appetite, research indicates the superiority of a higher frequency over a lower one.
In two separate studies led by Speechly, both lean and obese subjects had greater appetite control when pre-test meals were consumed at frequent intervals in contrast to the same amount of food consumed at a single meal (15, 16). In the ad libitium test meal that followed the pre-test meals, subjects given the single meal consumed on average 26.5 percent more calories.
Stote’s team compared one versus three meals per day (17). Among other results, the one-a-day group reported significantly higher levels of hunger and an increased desire to eat with the severity of both phenomena increasing throughout the length of the trial. In a recent alternate day fasting study (18), Heilbronn’s team concluded that: “Overall, these results suggest that a prolonged schedule of fasting and feasting would be marred by aversive subjective states (e.g., hunger and irritability), which likely limits the ability of most individuals to sustain this eating pattern.â€
Introduction
The ancient practice of fasting seems to periodically find its way into modern fitness subcultures. Despite its purported physiological and psychological benefits, scientific data is far from unanimously supporting it. Are there any physiological advantages to increasing or decreasing meal frequency? What are the downsides to intermittent fasting? What are the health advantages shared by fasting, exercise, and caloric restriction? Are there detrimental effects of resistance training in a fasted state? Anecdotal data is fraught with suggestion-driven bias so we will focus on what has been demonstrated objectively in scientific research.
Meal frequency—hot dogma and cold facts
Since the health nut culture’s infancy, the decree has been that one must eat every 2–3 hours, thus minimizing muscle breakdown while keeping the metabolic engine revving. Tupperware containers and coolers in gyms and cars were (and still are) a common sight, perceived by the public to be a sign of diligence and discipline. However, the long held belief in a higher-is-better frequency has been examined with the lens of science, and some interesting data has surfaced.
Effects on health and thermogenesis
Research indicates that a haphazard meal frequency, not necessarily a lower frequency, negatively impacts thermogenesis, blood lipids and insulin sensitivity (1, 2). Contrary to popular belief, a high frequency has no thermodynamic advantage over a low frequency under calorie controlled conditions (as opposed to ad libitium or free living conditions) using 24-hour indirect calorimetry (3, 4). So much for the magic of stoking the metabolic furnace with an extreme grazing pattern. It bears mentioning that lower 24-hour insulin levels as well as lower fasting and total LDL-cholesterol levels have been observed with higher meal frequencies (5, 6). However, in discovering this, studies have used unrealistic protocols for the higher frequency treatments, comparing three meals to nine or 17 meals per day.
Effects on body composition
With little exception (7,
, the majority of controlled intervention trials show no improvement in body composition with a higher meal frequency, with treatments ranging from 1–9 meals per day (9–11, 15). Unfortunately, a scarcity of research examining meal frequency’s effect on body composition under conditions of exercise exists in the literature. To further confound the data, results from studies are mixed. The singular, full length published controlled trial showing a body composition benefit of higher meal frequency (six versus three) is limited by its poor study design. In the trial, boxers consumed a 1200 kcal liquid diet over a two-week period (8). The six-a-day group retained more lean mass than the three-a-day group.In contrast to the boxer study, a recent abstract presented at the Twelfth Annual Congress of the European College of Sport Science reported the superiority of three meals a day to six meals a day for gaining lean mass during a 12-week period involving strength training (12). Too bad the three-a-day group also experienced a trend toward fat gain. This raises the possibility that the three-a-day group simply ate more calories overall. This wouldn’t be surprising, considering that comparative research shows an association of greater hunger with meal frequency reduction.
Effects on appetite
Studies indicating the disappearance or lack of hunger in dieters occur in either complete starvation or very low calorie regimes (800 kcal/day or less) (13, 14). Much of this data is irrelevant for most of you reading this. Furthermore, none of those studies systematically measured appetite throughout waking hours. Convenience issues aside, for the purposes of controlling appetite, research indicates the superiority of a higher frequency over a lower one.
In two separate studies led by Speechly, both lean and obese subjects had greater appetite control when pre-test meals were consumed at frequent intervals in contrast to the same amount of food consumed at a single meal (15, 16). In the ad libitium test meal that followed the pre-test meals, subjects given the single meal consumed on average 26.5 percent more calories.
Stote’s team compared one versus three meals per day (17). Among other results, the one-a-day group reported significantly higher levels of hunger and an increased desire to eat with the severity of both phenomena increasing throughout the length of the trial. In a recent alternate day fasting study (18), Heilbronn’s team concluded that: “Overall, these results suggest that a prolonged schedule of fasting and feasting would be marred by aversive subjective states (e.g., hunger and irritability), which likely limits the ability of most individuals to sustain this eating pattern.â€