Effects of eating frequency on metabolic rate.
Eating food six times a day or at a very high meal frequency doesn’t increase your overall metabolic rate more than simply eating three times a day.
If such frequency of meals can help you feel better on a diet, it may help, but it will not cause weight loss or prevent weight gain.
One side of the argument for “keeping metabolic rate up” with eating frequency implies that more frequent eating patterns increase metabolic rate.
A meta-analysis on eating frequency notes that “studies using whole-body calorimetry and doubly labeled water to assess total 24-hour energy expenditure find no difference between nibbling and pouncing.
Finally, except for a single study, there is no evidence that the frequency of meals alters weight loss in hypo energetic regimens.
We conclude that any effect of the eating pattern on the regulation of body weight may be mediated by the impact of food consumption in the energy balance equation”.
A review article conducted evaluating 179 abstracts (of which ten studies were deemed relevant for assessing meal frequency and weight loss interactions) did not find a significant relationship between meal frequency and weight loss, although they required more long-term evidence.
These results are found in other review articles on the subject.
Various individual interventions that modify the frequency of meals while keeping calories static find no difference in metabolic rate (24-hour energy expenditure) between the two groups. There was no change in weight loss at the end of the trial period.
When calories are significantly reduced, the metabolic rate decreases slightly but generally falls based on calories and not meal frequency.
A recently published article finds the opposite. When comparing three meals to 14 meals over 36 hours in a metabolic chamber in healthy men, there were no significant differences in total energy expenditure and a slight increase in energy expenditure. At rest in the lowest frequency group.
Increased frequency of eating and muscle gain
Not too many studies look at increased meal frequency and body weight gain. Still, limited evidence at this time (this section and the epidemiology section below) indicates that the observed weight gain is due to caloric intake—more than frequency.
Effects of fasting on metabolic rate
The other side of the equation for “keeping the metabolic fire fueled” implies that the metabolic rate can be depressed during “no eating” periods.
Short periods of fasting
After 36 hours of fasting, an increase in metabolic rate is observed (and does not change further when measured at 72 hours).
Epinephrine was found to rise at 72 hours (but not 36), and when measured at 48 hours, adrenaline appears to induce a more significant amount of heat production (thermogenesis).
In non-obese humans, alternate fasting (not eating every other day) does not decrease metabolic rate after 22 days (when ordered to eat twice as much food on the days they can eat to compensate).
Studies conducted during Ramadan also indicate an apparent lack of a difference in overall metabolic parameters between fasting and non-fasting.
Although some studies (especially those of people who are not healthy) show limited health benefits with the Ramadan fast if food intake remains relatively stable although it appears variable.
While the metabolic rate hasn’t been researched much per se, it doesn’t appear to change to a significant degree.
Possible Reasons / Data Harmony
Large-scale research shows a correlation between frequency of consumption and obesity, with the ‘nibbling’ approach inversely correlated with BMI (obese people seem to eat less, and thin people tend to eat more frequently).
These studies do not consider muscle mass per se, but rather BMI; There seems to be a trend for more meals per day to increase body weight and BMI. There is limited, conflicting evidence, which is confused with high activity levels.
In addition, the position of some nutrition agencies on the frequency of meals indicates that multiple observational studies do not suggest that the frequency of eating affects weight loss (at a fundamental level).
Some suggest a relationship is of interest, but the correlation is removed once confounding factors such as smoking, drinking, and stress are controlled, indicating that they may be the causal factor (s).
Additionally, eating frequency is positively correlated with overall caloric intake.
Thermal effect of food
The thermic effect of food (the energy required to digest food to obtain calories from food) is seen by some researchers as an essential long-term control point for obesity.
Erratic meal times, regardless of frequency, appear to be associated with a reduced thermic effect of foods.
Exercise has been suggested to be a confounding variable in epidemiological research due to acute energy expenditure and the movement’s ability to suppress appetite.
Survey Research Summary
Bottom line: Survey research shows an indirect relationship between meal frequency and weight gain due to an increase in calories overall.
A lower frequency of meals can be associated with a lower BMI (at the same caloric level) due to exercise.
There isn’t much evidence to suggest that meal frequency per se does anything good or bad for metabolic rate, but that’s just an epidemiological indicator of other habits that influence metabolic rate and weight changes.
A higher frequency of food consumption can be beneficial in preserving muscle tissue.
When comparing three meals against 14 meals per day (an extreme case), it was found that despite the same number of calories and no difference in metabolic rate.
The low-frequency group had a higher rate of protein oxidation (106.9 ± 7.1 vs. 90.6 ± 4.3 g / d) or 17% higher protein oxidation rates than 14 meals per day.
However, intervention in obese individuals noted that when four meals were consumed daily, there was no difference in weight loss when consuming 80% of its casein in one meal relative to pulsing whey in four 25% meals with the casein group.
This group outperformed the whey group in the final duration of the nitrogen retention test. This latest study observed higher protein oxidation and synthesis rates with whey but a trend toward casein’s nitrogen retention (muscle mass retention).
Theoretically, more meals a day may improve nitrogen retention. Still, a recent human study suggests that staying in a postprandial state is more important (which can be done with slower or more frequently absorbed proteins, or both).
One of the studies above did observe better glycemic control, as assessed by glucose AUC, in the group of 3 meals a day relative to 14 meals.
This has been seen before when comparing two meals per day versus 12, where the lower frequency appears to have better glycemic control.