The studies don’t seem entirely contradictory to me. The ones that say there’s no difference in weight loss (for people who eat some of their daily calories at breakfast, versus eating all the daily calories later in the day), aren’t measuring work done (brain work or physical exercise) in the post-breakfast hours. The focus of those studies was on the question of weight changes only.
The studies that say that eating breakfast does make a difference, seem to be looking at the issue of work (brain and/or non-brain) done in the post-breakfast hours–rather than looking at the question of changes in weight. The verdict there seems to be that having some of one’s daily total of calories during the breakfast hours IS helpful for getting brain work and exercise done.
The Consumer Reports article has a lot of “mights” in there … appropriately so and the recent two small studies mearly reaffirms the need to keep them there. Focus on small and not enough detail reported out. One was under 300 participants and one just 33. What breakfast consisted of was not reported out. Was it whole grain cereal and milk with berries? Or sugar bomb cereal? Or a stack of pancakes with syrup? Or a Greek yogurt with a not over ripe banana? It likely matters. It is up aginst observational studies (as reported in your cited article) “more than 100 [observational] studies have linked eating breakfast with a reduced risk of obesity” including ones 27,000 and nearly 30,000 subjects strong.
One of the studies found no impact on weight loss. Okay. One study thrown into the pool of data that is suggestive but not conclusive.
The other found that breakfast helps decrease inactivity. Those who ate 500 calories at breakfast moved around 500 calories worth more in the next few hours. Calorie-wise a wash but given that inactivity is associated with a host of adverse health outcomes a net plus overall I’d say.
Hard data still does not exist to beat people over the head with but my educated best guess is that a healthy breakfast (high fiber, high protein, low glycemic index) is going to be associated with a significant net benefit to skipping, even if weight is unchanged. That said there is a modest body of evidence that demonstrates some benefits to having no food for most of the day (variants of intermittent fasting) which most in practice effect by making a late afternoon or early evening meal a single meal of the day. I’d suspect that they’d be better off having that meal be earlier than later but the bottom line for now is … who knows?
The unstated assumption here is that vigorous exercise will deplete your blood glucose so nothing is left for your brain. That’s not how it works. Most cells, including muscle cells, don’t get to use blood glucose unless there’s a sufficient insulin level. If you don’t eat, there’s very little insulin so basically all the glucose released by the liver goes directly to your brain and nowhere else. Not sure if the brain uses more energy when you exercise, but I assume the difference is going to be small.
All the while, muscles will have to make do with the glycogen stored in them and the fatty acids they can obtain from blood. Burning fatty acids is less efficient, and I believe it even uses more oxygen for the same amount of energy, so running out of glycogen is the main problem with sustained exercise.
The brain can function just fine when fasting, it does that every night, unless you wake up in the middle of the night for a snack.
No offense but neither of your versions are all that accurate.
Muscles do indeed get to use blood glucose during exercise and there is plenty enough insulin around. To more accurate, muscles are directly fueled by ATP which they produce by the metabolism of intramuscular glycogen, blood glucose and blood fatty acids (relatively a slow trickle of energy). Glucose gets in more during exercise both because more is delivered (increased capillary perfusion) and because more gets put across the mebranes (through mechanisms other than increased insulin). More glucose is produced (as the muscles use up their intracellular glycogen stores and suck the glucose out of the blood) by breaking down liver glycogen.
A typical person has enough glycogen on board to handle at least 2 hours of moderate intensity activity (few exercise at an intense level for more than 70 minutes at a time) and a trained individual can have greater stores (and greater ability to use fatty acids along the way).
Exercise physiology nuts argue about how to eat when. Some point out that occasionally exercising with low glycogen stores can help train the body to use fatty acids more efficiently. And exercising before breakfast may have some other beneficial effects as well. Others point out that longer and more intense levels can be sustained if the muscles are as fully tanked up with glycogen beforehand. Most however agree that you should not too much right before intense exercise, maybe an hour or so before is better. Blood flow diverts from the GI tract during intense and prolonged exercise and too much in there will often cause some GI distress.
I am familiar with that article and it does not say what you think it says. The article does not find no link; it accepts the link as firmly established.
The focus of that article was about the language used in reporting science, specifically about the “inappropiate use of causal language” … their beef is that those more than 100 observational studies are just that, observational studies establishing an association. Observational studies can suggest causation but do not conclusively estabish it. The observed association is firmly established: those who skip breakfast tend to be fatter and have poorer outcomes and those who eat breakfast tend to be leaner and have better outcomes. They diss the publication of more studies that add to that as “lacking probative value” as it just further establishes what we already know. They further diss the language used in reporting these studies as implying an established causation. This, they argue, is inappropriate and reflects biased research reporting. Their position is that only randomized controlled trials can firmly establish causation and there are few of them that address this issue. Breakfast eating or skipping might be a proxy for types of foods eaten or other lifestyle or personality characteristics, for example.
Hence the importance of and attention paid to these very small and incomplete studies: they are randomized controlled trials. Again one that did not specify what breakfast was found that people randomized to eat breakfast or skip for 16 weeks had no differences in weight at the end. And another, that also found no difference in weight but found that those who ate breakfast moved more (burning off the additional 500 calories they ate at breakfast while not impacted how much else they ate) and had more stable afternoon and evening blood sugar levels. Reported out in the press as “see, eating breakfast won’t make you lose weight!” and ignoring the benefits observed.
Thanks everyone for your replies, especially DSeid. Exercise physiology has come a long way in recent decades, but still is a science in progress. As noted, the types of breakfast in the studies were not shown. From my personal experience, if I do my usual workout of an hour of running and nearly an hour of weights, I feel fatigued during my weight session, and I know it affects my workout. If I have my usual breakfast of oatmeal (with my add-ons of chia seeds, hemp hearts, frozen fruits, sliced banana, flax powder, and wheat germ)) with soy milk and a little maple syrup I feel much better. That breakfast also causes me to move my bowels within a few minutes after eating, so I do not have that urge while working out. Sometimes I will run with a friend who wants to run at sunrise, so I postpone breakfast then until after the run, and then I will do the weights. I feel fine for the run then. I will note, also anecdotally, that I never eat before a race, and when I was doing marathons, not even before a marathon. In those days these gels and energy packs were not available and all I drank was water and Gatorade if provided. One marathon around 1980 near Chicago provided only water as the conventional wisdom then was sugar would slow down water absorption. We now know (thanks to Dr. Noakes) that glucose in a 6% solution or less will not slow down water absorption. Since Dr. Noakes published his book (Lore of Running, I’ve read that it could be up to 10%. Does anyone have the straight dope as to the glucose solution?
There have been times I ate breakfast, lunch and dinner. Times I only at breakfast and dinner, times I only ate lunch and dinner and even times I only ate dinner. (With a bunch of snacking also, but rarely in the morning.) Throughout those years I gained a large amount of weight.
These days, I eat breakfast, lunch, a mid-afternoon mini-meal and dinner and I lost most of my excess weight.
For exercise, I cycle, walk and walk up and down stairs. I’m pretty sure I can tell when my glycogen is depleted with the stair walking, which becomes rather difficult when that happens. As I’m on a calorie restricted diet, I reach this stage after 10 - 30 minutes. On my bike or when walking, it’s several hours before I notice I start to slow down a bit but it’s not too bad.
I certainly don’t do my best thinking when exercising (research shows that moving your body takes a lot of brain power and impairs higher functions to some degree), but I don’t think my brain suffers from lack of energy at any time, even when the rest of my body does.
My advice regarding breakfast: if you don’t eat breakfast and you’re happy with your weight and how your body functions: good for you. But if you don’t eat breakfast and you’re trying to lose weight and/or find yourself scarfing down terrible food later in the day and/or suffer from a lack of energy at some point in the day, maybe it’s time to heed the correlation between maintaining a healthy weight and eating breakfast, and try eating breakfast yourself. If eating first thing in the morning is unpalatable, eating an hour or two later still counts as breakfast, so try that.
FWIW I’ve tried to do a small literature skim and the bottom line seems to be that up to 8.6% is possible and best in a 2:1 glucose to fructose ratio. Beyond that they state GI issues become more frequent. That 2:1 glucose/fructose combination does seem to result in faster gastric emptying and improved delivery of both carbs and water than just water alone or all glucose in the same concentration.
For the wonk wannabe this seems to be a pretty exhaustive review. Pretty much the same bottom-lines with some neat little additions:
First the same information in a bit more detail:
For events (or training sessions) under an hour there is no real metabolic impact from ingesting additional carbs BUT there do seem to be centrally mediated impacts: these can be acieved even by quick mouth rinses with no carbs ingested at all -
Finally the issue of potential benefits of training low at least some of the time in order to force adaptations tha utilize fatty acids more efficiently …
Important for those of us who just exercise for fitness or recereationally or as week-end warriors? Probably not. And afterall, as those authors point out: