Large or Small Meals?
Do a quick run-down of all the things you've hear about meal size, I'll wait.......
Did you come up with any "facts" like small frequent meals stoke the metabolic fire, or you can't eat a large meal past 6PM or that you cannot absorb more than 30g protein per meal?
All hogwash I say! But where do these ideas come from and what does the science actually say about meal size?
Last time I checked, we do not run on internal combustion, like cars. So to that end, comparing our metabolism to a fire is downright sily. Especially considering fires need oxygen to burn and we have anaerobic (without oxygen) metabolism capabilities. Secondly, we do not function like an engine where you simply put in some fuel, fill up the tank and you're good to go until the next fill up. We have multiple energy systems, energy storage capabilites and the ability to use MANY things for energy (from food). I did write the word "energy" three times and it seems some people confuse that with "fuel", hence the car analogy.
But I think those simplifications do way more harm than good because it causes us to view our body and physiology as a simple Input:Output relationship when in fact we have so many more factors to consider like age, stress, past history, weight, sex, activity, goals and more. So yeah, you could "fuel up" but context is everything.
A Quick Example
Some years ago I saw a late night advertisement for some fat loss product, I honestly cannot recall it in the slightest. But I can vividly recall the dramatic scenario of the commercial that was intended to lure you in. In this commercial, it was late at night under the stars and 10-12 people were sitting around a campfire. One man is standing and he is explaining your metabolism is JUST LIKE (eye roll) a fire. #firebody?
But of course these commercials are meant to be dramatic and compelling and using a visual medium is sure to suck people in. So he explains eating small, frequent meals is like putting some kindling on the fire.....it quickly consumes them and grows hotter. He throws some small branches on the fire and it grows in size. Then he explains that a large meal extinguishes that fire as he heaves a giant log into the flames which nearly puts the fire out. Wow, bravo I am nearly standing and clapping at his performance.
And this is the level of expertise we are being led by, catchy and compelling advertising that has no real basis in science and like all of these programs, ends in you being frustrated and worse for wear.
Checking Under the Proverbial Hood
I know, I know, a car pun, really?
One of the biggest reasons you'll hear claimed that large meals are inherently bad for fat loss is insulin. It goes like this:
Insulin is a storage (or rather a nutrient mediator) hormone. It directs energy storage in the body. Glucose to muscle tissue, glycogen storage in the liver, storage in fat tissue and overall clearing glucose from the blood stream.
When insulin is present in the blood, fat cells cannot undergo lypolysis which is the breakdown of triglycerides into free fatty acids and glycerol which are released into the blood stream to be utilized for energy. So, you can't burn your body fat when insulin is hanging around.
Small meals = smaller insulin spikes
Large meals = large insulin spikes
Again, we're back to simple analogies. If you think insulin is BAD, then more seems like the wrong path, hence small, frequent meals. Small meals net a smaller insulin rise and is cleared from the blood sooner, meaning you can quickly get back into "fat burning mode" as people love to call it.
Research Says Probably Not
Small or Large?
Service Et al (1) conducted a study on six lean, healthy young subjects which had them ingest similar foods in varying amounts: Either 12.5%, 25% or 50% of their daily calories per meal. They had them eat the meals smaller to larger during the day, then reversed that on other days. The goal was to see if meal size at certain times had any effect on insulin and glucose above what would be expected. One big take-away is researchers noted there was a corresponding insulin rise as meals got larger....that's good because that makes sense. Blood glucose also rose higher after larger meals. So again, this falls in line with what we'd expect. Essentially, smaller more frequent meals have smaller and shorter insulin spikes and large meals have the opposite. But overall the insulin and glucose rise is the same over the course of the day whether you have 6 small meals or 3 large. If you consume 3 large meals you have a great rise in insulin and glucose but then longer time between meals where there is no insulin present.
Think of it like this: if I give you one dollar six times per day it's the same as two dollars three times a day. In the end it's 6 dollars, your preference is the main factor.
And if you're Type 2 Diabetic?
Hana Kahleova in Prague(2) conducted research on type-2 diabetic patients (so we're not talking healthy subjects here) and found they had better blood glucose control on two large meals a day compared to six small. Interestingly, researchers had them all consume a diet around 50% in carbohydrates which is more than you'd expect for a population with poor blood sugar control. But all subjects ate at a 500 calorie deficit with the same exact percent macros.
Despite insulin secretion rising similarly in all patients, all patients saw insulin sensitivity improve and liver fat decrease. But the two meal per day patients lost over 8lbs compared to 5lbs for the six meal per day patients. What we are seeing here is that fat loss and insulin sensitivity can STILL occur with a relatively high carbohydrate intake but a calorie deficit is the main driver of your results. It's important to take away that even with a bunch of small meals AND impaired insulin sensitivity, a calorie deficit is a powerful thing for results. We also see that if insulin sensitivity is an issue you might have a slight edge in larger, less frequent meals.
Is age a factor?
Melanson et al (3) compared post-prandial (after a meal) insulin and glucose concentrations at various time throughout the day. They had all female patients divided into two groups: young menstruating and older post-menopausal. Like a lot of these studies, the carbohydrate intake was kind of high - 60%!
There were no significant differences in post-prandial glucose and insulin rise between the younger and older women. However, there was a divergence towards the older population having poorer glucose/insulin responses after larger meals, about 500 calories and up. When the older women exceeded 500 calories per meal, they had longer periods of elevated blood glucose pointing towards a slight insulin resistance.
This is not shocking though, as hormonal changes post-menopause impair insulin sensitivity with testosterone and progesterone being higher and estrogen being lower. Also, most older women are less active and carry less muscle mass than their younger counterparts.
Making Sense of This
In essence, we're seeing here that in lean and active clients, meal size has pretty much no adverse effects on insulin sensitivity or blood glucose control. If you're healthy, you see a larger spike in insulin after a big meal but the return to baseline is still pretty fast. And the overall insulin and blood glucose concentrations are pretty even overall for the day, whether it's 6 small or 2-3 large.
In clients with impaired insulin sensitivity, the largest factor in weight loss success is creating a calorie deficit. Even with a higher carbohydrate intake (50%) people still see an improvmenent in insulin sensitivity. And it seems like the edge may go to fewer, larger meals for these individuals when it comes to overall fat loss. This could be due to the nature of fewer insulin spikes resulting in a slight edge towards increased sensitivity.
When age is a factor, your ability to manage a large meal usually decreases. But this is not unexpected as the older you are, the less your daily energy needs as muscle mass and activity are usually less. Many older people inherently eat smaller meals as this might just "feel better". But if you matched their energy intake to their needs it's probably not a big deal whichever way you choose to go.
In the first study, the only real variant was a large meal at night - it tended to have the worse blood sugar and insulin response. Researchers point towards a decreased insulin sensitivity as the day progresses meaning a large meal late in the day causes blood glucose to stay elevated longer with insulin being slightly impaired. But for fat loss I am not sure if this is a huge deal as
1. Your calorie deficit will control whether you lose or gain
2. This might be whole-body insulin sensitivity meaning fat cells are less likely to uptake the glucose as well and
3. The large meals in this context were 50% of the subjects daily calories which is well above what most people would eat in a single meal, meaning this is probably not an issue for 99% of people
The meal size that had the same glucose and insulin effect regardless of time of day was 12.5% of the subjects calories, meaning they'd be eating 8 meals per day. So if you want the most consistent blood sugar and insulin response you could eat 8 very inconvenient, very unsatisfying and very impractical 8 meals per day.
Notes on Blood Sugar
I'll note that blood glucose in healthy people doesn't just rise uncontrollably with the size of a meal. Sure, we see it go up as a meal gets larger but if blood glucose after a small meal is 7.5 mmol/L, it will not double to 15 mmol/L if the meal doubles in size. This shows how tightly regulated our blood sugar is. Instead you will simply see a longer and smaller blood sugar elevation with a large meal and that's perfectly normal and healthy. Remember that between meals you've got about 4g (one teaspoon) of glucose in 5 liters of blood. That's a pretty regulated system.
Take Home Points
1. When calories are controlled, the overall impact of small or large meals is marginal
2. A calorie deficit creates better insulin sensitivity than drastically cutting carbs
3. Age, muscle mass, body fat and activity all play roles. Generally if you're older you might not feel great eating huge meals so go with what feels good
4. Don't eat meals so small that you cannot get significant protein in. A 200 calorie meal doesn't allow for much protein so eating like a bird will be a pain in the butt for gaining muscle and recovering
5. Eating late vs early shows some difference in insulin sensitivity when comparing large meals, but unless you're eating over 50% of your calories at night in one sitting, it's not an issue
6. Losing body fat improves insulin sensitivity and blood sugar control, NOT just cutting all carbs (REMEMBER THIS!)
7. Stay active, train for strength and muscle, lose weight if your insulin sensitivity is not good and eat the number of meals that is practical for you while allowing for enough protein AND a calorie deficit