Metabolic impacts of altering meal frequency and timing- does when we eat matter? (Link to full article at end)
This one a doozy guys– with 140 cited references. Papers like this are super cool though because instead of reading 140 papers- I only need to read one to gain a feel of the overall trends of the research.
I am going to start with the most important statement, IMO, of the entire study.
“Practically, dietary adherence to any intervention remains of primary concerns in the population, and it may be that no one dietary recommendation suits all.”
I think that is the perfect way to preface the following discussion. In research design, we are literally trying to eliminate individual differences between people (and between groups) so that we can isolate the impact of one particular variable. This has obvious complications and limitations- as in real life, we are all very different and we rarely ever change only one variable at at time— so while research may suggest that a certain dietary pattern is optimal for weight loss- this does not necessarily mean that it is the optimal strategy FOR YOU given your unique set of personality traits, training/ aesthetic goals, life stressors, etc. Whew. That was a mouth full. So here’s some of the key points from the paper.
This paper reviewed the evidence for modified meal frequency and timing on appetite regulation, body weight, energy metabolism, and metabolic health parameters- including glycemic control and lipid profiles. They also investigated the role that circadian rhythms play in mediating the physiologic responses to a meal- pay attention if you do shift work.
Take away points with more details below:
1. and 2. Meal frequency does not impact daily energy expenditure (increased or decreased)
3. Observational fasting studies show some metabolic benefits!! It is difficult to parse out what effects are attributable to the caloric restriction that tends to occur with fasting practices versus those that are a function of the meal timing associated with fasting.
4. Eating a large portion of calories at night (assuming you’re not eating in a caloric surplus) does not appear to have any adverse effects. Definitely more research needed here- many of the studies discussed were short term studies.
5. Circadian misalignment (aka being awake during night time hours) is less than ideal for health markers and can completely reverse diurnal cortisol rhythm.
1. Evidence supports that meal frequency does not impact daily energy expenditure. Translation- your metabolism doesn’t “speed up” more if you eat more frequently throughout the day. Evidence also suggests that if you’re existing in a caloric surplus more frequent meals can lead to increased abdominal fat and reduced insulin sensitivity. Here the overall main theme is how much you are eating- with the timing of those meals having a smaller impact than the overall caloric intake itself.
2. So then, does reduced meal frequency or time-restricted feeding (TRF) differentially impact appetite, body weight, and metabolic health? One RCT (with women!! Yayyy a study of women!!!) which reduced meal frequency from 3 to 2 found that having fewer meals reduced feelings of satiety throughout the day. In obese individuals, consuming 1 meal/ day for week resulted in greater weight loss than consuming 5 meals/ day- with calories being equal. Another study of obese women found no differences in body weight, fat free, or fat mass in those consuming 2 meals/ day as compared to those consuming 3-5 meals/ day. Overall reducing meal frequency does not appear to impact weight loss or energy expenditure in human studies.
3. So what about fasting?!? Fasting depletes hepatic glycogen, reduces glucose and insulin and produces a switch toward ketogenesis, lipolysis, and lipid oxidation. Fasting also activates the cellular and metabolic processes that reduce cellular damage in animal models- all of which may contribute to the health benefits of fasting diets. Many of the studies of time restricted feeding (TRF) in humans are from observational studies- particularly of those fasting during Ramadan. Studies reporting on these fasting practices (with fasting taking place from dawn to sunset) report improvements in blood lipids including reductions in total and LDL cholesterol, triglycerides, and increases in HDL cholesterol. The authors state that these benefits are likely due to the caloric restriction associated with these practices- not necessarily the meal timing itself.
4. Currently, the evidence is inconclusive about the effects of eating a large portion (>33%) of your caloric intake in the evening on body weight and metabolic health. What we do know is that consuming a larger portion of calories at night is associated with a larger caloric intake overall- so any metabolic health effects are likely due to the increased caloric intake- not necessarily the practice of eating more at the evening meal.
5. What about shift work? What about eating meals when our body thinks we are supposed to be asleep? We do know that shift works are at a higher risk of metabolic disorders, including obesity and DMII. We also know that prolonged exposure to circadian mismanagement (aka being awake during the night time hours) can lead to poor glucose tolerance and can alter the diurnal cortisol rhythm.
Papers like this also tend to leave us with more questions than we started with!! What questions do you guys have? Let me know so I can keep reviewing the literature for you!