We’ve all heard it before: if you want to boost your metabolism and lose some weight, you need to be eating smaller meals more often.
This way of thinking has been around for decades. You can trace it back to some studies done in the 1960s showing the more frequently a person eats, the leaner they become.
More recently, we’ve completely shifted the way we think about meal frequency. Now, it’s all about intermittent fasting. That is, abstaining from food for an extended period of time – maybe 16-18 hours – then eating the remaining calories within a 6-8 hour window.
These two ways of thinking are in direct contradiction to one another, which doesn’t leave a lot of room for a middle-ground or gray area. One of them has to be better than the other.
With this article, I’ll take you through how each type of diet affects your metabolism. Then, you’ll have plenty of information to decide which one seems better for you.
The effect of increased meal frequency on metabolism
Metabolism can be altered in one to four ways:
- Altering the basal metabolic rate (the minimum number of calories your organs need to function while you perform no activity whatsoever)
- Altering the thermic effect of food (the energy you expend to process food you eat)
- Altering the energy expended due to exercise (the energy you expend due to physical activity)
- Altering something called “non-exercise activity thermogenesis” (the energy you expend during daily living that wouldn’t be considered structured exercise)
To date, there is no research suggesting increasing the number of meals you eat in a day will alter any of these factors.
Benefits associated with increasing meal frequency are most likely secondary to beginning to control caloric intake. Once you begin to pay attention to and control the number of calories going in, you may experience a reduction in body weight and a change in body composition.
Once this reduction happens, then you begin to see changes in the factors that relate to metabolism. For example, a decrease in body weight is associated with an unconscious reduction in spontaneous activity, which is a reduction in non-exercise activity thermogenesis, and, therefore, a decrease in energy expended.
It has been speculated that an increase in meal frequency could increase non-exercise activity thermogenesis because you’re active preparing more food throughout the course of the day. But, the increase is likely negligible.
Controlling caloric intake can cause changes in body composition (i.e. increase the relative proportion of fat-free mass).
Your basal metabolic rate is largely dependent on the amount of fat-free mass you have. So, increased meal frequency can increase basal metabolic rate, but, again, it’s secondary to a change in body composition.
The effect of intermittent fasting on metabolism
Intermittent fasting is a broad term describing multiple different protocols for regular short-term fasts. Intermittent fasting, like increasing meal frequency, does not alter metabolism with respect to the four factors mentioned in the previous section.
And, again like increased meal frequency, intermittent fasting is associated with increased control of caloric intake and body weight reductions and body composition changes. So, there will be some changes in metabolism secondary to these two factors.
What intermittent fasting does do, which increased meal frequency does not, is alter the substrates which are utilized to supply energy.
Normally, the body relies primarily on carbohydrates to maintain the four factors involved in metabolism: basal metabolic rate, the thermic effect of food, energy expended due to exercise, and non-exercise activity thermogenesis.
Short-term fasting switches the body’s reliance on carbohydrates to fatty acids. This is exemplified by decreased blood glucose levels (signifying a decrease in the use of carbohydrates) and increases in markers of fat oxidation (meaning an increase in the breakdown of fat).
How does this shift from carbohydrates to fat utilization occur?
It’s thought to happen through increased sympathetic nervous system activity, more circulating growth hormone, and decreased insulin.
The sympathetic nervous system is a branch of the nervous system responsible for initiating the fight or flight response and maintaining normal functioning in various organs and tissues throughout the body. It does this through various neural connections.
The sympathetic nervous system has connections with the liver and fat tissue.
Stimulation of the sympathetic nervous system (which happens with intermittent fasting) increases fat breakdown in fat tissue and stimulates the liver to use more fatty acids to create VLDL-TGs.
Growth hormone is a hormone known to increase fat breakdown when its circulating levels are increased. This hormone increases during intermittent fasting.
Insulin, a hormone mainly responsible for the uptake of glucose into the liver, fat, and skeletal muscle cells, also regulates fat metabolism. High insulin levels promote the synthesis and storage of fat, while, put simply, low levels have the opposite effect. Insulin levels decrease with intermittent fasting.
The bottom line
Neither increasing or decreasing how often you eat leads to an increase in metabolic rate. Any differences in metabolic rate noticed with either diet seem to be as a result of increased calorie control, reductions in body weight, and changes in body composition.
That being said, intermittent fasting seems to have some clear advantages when it comes to substrate utilization (i.e. using fat as an energy source rather than carbohydrates).
There you have it. You should have enough information about both types of diets to make an informed decision about what diet will work best for you.
If you’d like more, or some personalized help, please contact me. I’d love to share what I know with you.
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Thanks for reading and have a great week!