Hacker News new | past | comments | ask | show | jobs | submit login
Exercise elicits superior metabolic effects in the afternoon compared to morning [pdf] (nih.gov)
55 points by prostoalex 34 days ago | hide | past | favorite | 60 comments

I understand the desire to investigate stuff like this, but for 90%+ of people, every inquiry in to "most optimal way to not be debilitating unhealthy" is just a waste of time.

If you're not in a special group (gout, hypertension, allergies, etc.) the answer is incredibly simple:

- your diet determines your size

- your activities (or lack thereof) determine your shape

I realize that type 2 diabetics (as being studied in this paper) might be considered one of those groups, but as far as I can tell, almost all of the war is in getting people wanting to improve, and very little of it is in the how to do it.

Maybe that's just me, but I feel like we're searching for our keys under streetlight here. These are easily studied problems, so there are papers/book written. Trying to understand the myriad psychological and societal (and possible environmental) processes is where the real gains will be made.

> as far as I can tell, almost all of the war is in getting people wanting to improve, and very little of it is in the how to do it.

I get it. I agree with you regarding the war.

That said, as an individual that already tries to be healthy, I find the scientifically rigorous “how to do it better” is typically missing. I’m very grateful for a study like this, even if it’s not perfect and I need to extrapolate for a non-diabetic like myself.

>your diet determines your size - your activities (or lack thereof) determine your shape

Damn. This is really well stated. With all the hundreds of fitness experts and personalities on the Internet and YouTube, it actually just comes down to this.

People also say "your body is made in the gym, but revealed in the kitchen".

It's a bit of a simplification, but it requires so much exercise to burn the calories in a snack, it's easier to just not have the snack in the first place.


A blueberry muffin is around 424 calories. It takes about 45 minutes to burn that many calories jogging.

Compare that to how many minutes it takes to simply not eat that muffin.

A lot of people are afraid of the feeling of ‘hunger’; I find the sensation of hunger is actually a motivating one. I try to fast around 16 hours a day (eating window 12pm-8pm) and really think it keeps my head clear and helps me work, especially in the morning.

Based on my personal experience, I think there are two feelings which are associated with "hunger".

The first one seems to be triggered by eating relatively-high carb and calorie-dense foods. Say Snickers bars. This feels like a sudden loss of energy and a want to eat something. What's interesting is that the feeling seems more like a craving for something "fast and sweet", like another chocolate bar. I specifically don't feel like eating a "regular" meal. It also seems very intrusive mentally. I can't think about anything else except going looking for that next treat.

Then there's what I'd say is "actual hunger", which to me feels very, very different from the first. It's usual not accompanied by a lethargic feeling, and like the parent said, there seems to be some kind of motivation and (what at least looks like) increased mental acuity associated with it. This seems to go away after 30 minutes to an hour, and usually only comes after having fasted for a while and / or having exercised. When I get this kind of hunger, I usually don't even consider chocolate bars or similar as "food". I usually think about having a fairly substantial meal, usually some kind of vegetables, protein and fat. Like butter, chicken / steak, some broccoli or other salad, etc.

I've found that by reducing sugar consumption -- not to 0, I've never gone on a zero-carb diet -- especially in calorie-dense foods such as industrial "treats", the first kind of hunger rarely, if ever, shows up. And I actually rarely, if ever, feel like eating those things. Whereas some 10 years ago, when I'd eat a lot of Snickers bars (I used to really love those), the feeling would show up multiple times a day and would be a real bother mentally. My energy levels also seem much more stable throughout the day now.

While there are several different physiological effects that contribute to what we call 'hunger', what I suspect you are describing is mostly related to different blood sugar profiles.

When you eat foods which are simple-carb based (i.e. sugars, or other small, easily-digestible carbs) your body can very quickly and easily utilise them, resulting in a fairly rapid spike of blood sugar. Importantly, because they're easily-digestible, their sugar will be released over a short period of time. In response to the sugar spike, your body will release insulin and drive the sugar out of your blood stream, but because the flow of new sugars from your gut has slowed or ceased, this can result in quite a low blood sugar state. When you hit this state, you not only feel very hungry, but also crave foods which will give you quickly-available blood sugar, to resolve the situation quickly. One other point is that while your body has the ability to release sugar (or other substances which similarly give you energy) from stored reserves, these processes are fairly slow - so don't really respond quickly enough to account for this sort of sudden low sugar state.

In contrast, if you eat a more balanced diet (with complex rather than simple carbs, some protein, some fat, more fibre) you change both parts of the previous effect: the spike of sugar into your blood stream is less pronounced, because the food you've eaten is less suited to provide it, and also the release of sugars occurs over a longer period. So you don't get the sugar spike, or the big hit of insulin in response, or the low afterwards which makes you crave fast sugars. And also, because this is all slower, thanks to eating foods which provide a slower release of nutrition, your body's systems have an opportunity to work alongside your food, and as (for example) the release of nutrition from your gut slows, offer nutrition from your body's stores to sustain you for longer.

That's an interesting division, because I also think of "first" and "second" hunger, but differently.

What you describe as "actual hunger" is what I think of as "first hunger", which is just triggered by mealtime, and goes away after 30 minutes to an hour as you describe.

If you ignore that sensation of hunger for about a day, you start to feel a deeper sensation of hunger which doesn't go away, it just keeps growing.

If I may be permitted to indulge in some "just so story" pontificating:

Hunger type 1: "Gathering". There's berries out there, dammit! Stop wasting your time and eat em before the birds do.

Hunger type 2: "Hunting". It's time. Sharpen your spear. Focus. Run. And if you catch nothing, we'll try again tomorrow.

While I get your point, I find it somewhat amusing that berries — and whole fruit generally — will actually not trigger this kind of reaction.

And if you think about it, in kinda makes sense.

A "large" banana has 121 calories for 136 grams [0].

A Snickers bar has 245 calories for 48 grams [1].

I think this kind of difference messes up the body's perception. Even honey has less calories than a Snickers bar [2]. I, for one, can't eat too much honey without feeling like I've had enough. But I can easily eat two Snickers bars one after the other.

Maybe we just haven't evolved to handle such a high concentration of calories being so readily absorbed from so little food.

This could explain another commenter's point: "we shouldn't have to count calories, the body should be able to handle that on its own".

Well, I suppose it does, but it handles that based on some assumptions which clearly don't hold in some situations. Of course, it's also not easy to "will" yourself into doing this. Suppose you eat 9 Snickers bars a day, which is more than the standard 2000 calories for a male. I'm pretty sure someone eating that would still feel hungry all day long.


[0] Calories in a banana: https://www.healthline.com/nutrition/bananas-calories-carbs#...

[1] Calories in Snickers bar: https://www.sainsburys.co.uk/gol-ui/product/single-bar-choco...

[3] Calories in honey: https://www.caloriescalc.com/honey/

It is crazy how our modern culture normalizes eating all the time. Our bodies were not designed to process an endless stream of calories. Our whole relationship with hunger is out of whack.

I remember eating a protein bar while backpacking after being fatigued and heavily calorie restricted for a few days. While eating, I had a very acute sense of how precious the blessing of food was. I recognized how this thing we constantly take for granted saved me from a pretty miserable existence.

I agree with the feeling of working while fasted. I find that I am not as productive after I break my fast for the day.

> I try to fast around 16 hours a day (eating window 12pm-8pm)

I've been doing intermittent fasting for ~5 years now, and I don't even feel the hunger anymore. The only time I feel it is when I aggressively work out (running ~2 miles in the morning + lifting ~45 mins in the afternoon 5 days a week) and if I'm on a caloric deficit (~1750kcal). I also notice I get that hungry feeling particularly if my macros shift away from carbs (which they usually do when cutting weight). The human body is an incredible machine.

Have you tried upping your fat when you are cutting? I find that my hunger tends to be controlled mainly by my fat intake.

I haven't, but maybe I'll give it a try! Unfortunately, there's not that many fatty foods I actually enjoy eating. A lot of people like avocados but I can't stand them, for instance. Same story with peanut butter.

similar, but we always used to say "abs are made in the kitchen, not in the gym".

'Incredibly simple' answers and platitudes do an immense disservice to anyone trying optimize the effects of diet and exercise. For example, high-intensity interval training has been shown to be far more effective than low-intensity. And many have found a starvation diet is impossible to maintain and far less effective than a keto diet. It may seem like a waste of time to you, but this type of research can add up to important shifts in how we understand and maintain health.

Agreed. Gary Taubes has written three high quality books on the subject. The most technical and heavily referenced are Why We Get Fat and The Case For Keto. The latter was just published.

I’ve been following a low glycemic diet for decades, but Taubes explains technically why it minimizes fat deposition.

If I start eating snacks like candy or corn chips, the weight gain is immediate and obvious. Not all calories are the same - some foods just “go to your hips”.

Eating low carb and switching to high carb will cause significant water weight increase due to increased muscle glycogen. On the order of 5-10lbs. It's not fat.

That’s correct. For me, the effect is about four pounds. It comes off as fast as it went on.

But if I continue to eat high carb, there is a weight gain that is much harder to shed.

Are you saying that a diet from higher carbs will produce more fat gain than an equicaloric low carb diet?

Yes, I am saying just that. The body uses 100 calories of corn chips and Coke differently than 100 calories of bacon eaten by itself.

Read Taubes for references to the scientific literature.

The first law of thermodynamics takes issue with this. A calorie is a unit of measure for energy.

Excess calories can be stored as fat. Carbs that drive high insulin levels end up being converted to fat, and the subsequent low blood sugar level promotes more carb consumption.

This does not happen with protein and fat consumption. If you force yourself to overeat those foods in the absence of carbs, which is not easy, they will be simply eliminated.

You're saying that eating excess calories in the form of fat won't be stored as fat? That's the most efficient pathway and was critical to our survival.

What you're referring to (excess carbohydrates converted to fat) is denovo lipogenesis which is exceedingly inefficient and rare in humans.

My personal experience over several decades aligns with what Taubes explains in the first book I cited. If you want the technical details, you could read it.

You can't get fat on a diet that is strongly deficient in carbs, while it's easy to get fat on a diet containing high proportions of fat and carbs.

The Eskimo subsist on meat and blubber alone. Roald Amundsen ran the experiment on himself and confirmed it.

The group of people you're referencing (Inuit people btw, Eskimo is a slur) have some of the highest obesity rates in the world! The Nunavuts have an obesity rate of 48%!

The ethiopians have a diet of mostly carbohydrates (>70%), and are extremely lean.

Taubes is a bullshit artist who cherry picks data to sell books.

Modern Inuits. Fast food. And stuff your 'slur'. !w Eskimo.

Ethiopians are hungry.

Not the person you addressed, but people are not lab rats whose daily caloric amount is controlled by a lab technician.

We humans in rich countries eat ad libitum. Any dietary intervention that helps us feel less hungry will lead to a reduction in the calories we consume.

I never said they didn't. I said that a diet, when controlled for calorie levels, will yield identical fat gain/loss.

Of course not. The type of foods you eat affects how many calories you eat so the diets won't be equicaloric.

Well the person I responded to is claiming equicaloric diets lead to different levels of fat gain.

Effective for what? Body composition? Fitness? If the latter, please explain why all elite endurance athletes do the overwhelming majority (>95%) of their training at low intensities. If the former, well, elite endurance athletes sure aren't fat.

First, I would like to see a source for your 95%. That sounds fishy. Almost every sport I can think of incorporates high intensity interval training and did before it became common for the layperson to incorporate in exercise regimens.

Second, what elite athletes do often does not translate to what laypeople can and should do. Most elite athletes have a tremendous gene advantage over other people, not to mention the time, energy, diet, coaches, etc., that allows them to push beyond what the average person can tolerate. It's almost ridiculous to say, "Micheal Phelps does xyz in the pool and you should too if you want to improve your health in the most efficient way possible."

What is the cutoff for elite athletes vs non-elites? A 5 minute mile? 6 minute mile? Why would there be a discontinuous jump between what a lay person should do versus a profesionally athlete? Sure, volume and intensity would be scaled back but type of exercise wouldn't be all that different.

See https://bodyrecomposition.com/training/endurance-training-me... for an example. The German track cycling team does 90+% of their training at low intensities. For an event lasting 4 minutes. The simple fact is that at the highest level, all pure endurance athletes do mostly aerobic work.

Ok, I missed where you were referring specifically to endurance athletes. You may be correct that endurance athletes do most of their training at lower intensities, although they almost all incorporate some type of higher intensity interval training.

The reason I separate elite athletes from others is that they are genetically different than the average person. To be an elite athlete in a super competitive sport, you are not representative of the normal population. You can likely train harder and longer and most likely have some type of other genetic advantage. It's far better to focus on studies that look at normal people rather than elite athletes.

Anyway, to go back to your original question, asking how HIIT is more effective, you are right that it is not necessarily effective at every endeavor. But literature shows that for the average person, doing 10 minutes of HIIT can be as effective in losing weight, gaining muscle, cardiovascular fitness, etc. as doing something like 30 minutes of low-intensity exercise.

> I understand the desire to investigate stuff like this, but for 90%+ of people, every inquiry in to "most optimal way to not be debilitating unhealthy" is just a waste of time.

95% of people won't program their exercise based on random studies, so I'm not sure what the conflict is.

>almost all of the war is in getting people wanting to improve, and very little of it is in the how to do it.

This is ultra naive. In the long term, 'wanting to improve' has to translate into compliance. getting people to want to improve is a short term thing that changes when you have to get up an hour early to run and shower, or whatever they choose.

Getting people to comply long term is incredibly difficult. You can succeed in getting people to want to change and still fail long term compliance and get nothing.

>Maybe that's just me, but I feel like we're searching for our keys under streetlight here.

I don't think 'we' are one group, looking at only one group, for one particular reason. 'we' are an entire world full of people doing research for different reasons on different things.

IMO health industry manufacturing trendy shifts from weak exercise science is large source of misunderstanding. Particularly when optimizations are exercises in minutiae. Fundamentally exercise + diet is simple but not easy.

Not easy generally attributed to adherence and effort, but not easy also because individual response curves and almost every intervention works for some cohort while not others as you highlighted.

What's really missing are better structured exercise plans that guides individual experimentation via roadmap from most effective -> least affective. Not major in minors, while constantly changing minors. Currently most people just bounce haphazardly from one fad to another, frequently mid-fad while biological processes from one response cause conflations.

I agree thee kind of papers seem like a hairsplitting contest.

Especially if you talk to people who ACTUALLY and SUCESSFULLY control their size... for (non hardocre) bodybuilder its pretty much IIFYM and for fighters who cut for fights its "just eat less bro, yes its hard.. are going to complain lol ?"

Remember, diet composition effects size, not some weird obsession with "calories in calories out" in some non-scientific cargo cult way.

Calories in, calories out absolutely work.

Except that humans don't manage their diet by counting calories. We have regulatory mechanism that supposed to do the calories counting for us.

The other replies to this comment are examples of what I was talking about.

Do different foods have difference metabolic properties, including variations in accessible calories? Yes.

Can we accurately measure calorie intake? Kind of. Even with a food scale, I'm not sure we get to within 10% of the "correct" calorie count because the methods for determining the calorie / lb may have issues.

Could people do weird things, like wrap food in cellophane, burnt it before eating, or even just throw it all up? Of course.

But so what? We have a real world problem here in that Americans (and others) are suffering a material degradation in quality of life due to health issues related to diet and exercise.

There are tons of optimizations possible, but they don't matter to cohort in question. For them, CICO is good enough by far. These optimizations are like trying to teach matrix math to someone who can't add--and doesn't want to learn.

Yet, I regularly see these discussions veer into the realm of these optimizations, presumably because the real problems are too hard and/or depressing.

What I am saying that CICO and nutrition labels shouldn't matter because humans aren't supposed to or need to count CICO because our biology should be assisting us to balance it out.

The fact it's not working means something's broke.

Counting calories absolutely work for weight loss. I haven't done it and reaped the benefit of it, but ultimately it wasn't sustainable for me.


My main point was that people don't want to talk about the main issue, but rather these details.

The fact that natural hunger/satiation doesn't seem to work anymore certainly counts as a main issue (and you got some off topic replies).

Thinking about "what's broken" though, I have a few hypotheses:

1. We're surrounded by supernormal stimulatants that are hijacking our brain. (While this is possible, most of the worst food was available before the recent spikes in obesity)

2. Economics: calories (in any form) used to be expensive, so only the rich could get fat. The skills required to thrive in a world that doesn't impose calorie restriction at some level are just not widespread.

3. Our internal systems can't function in a world where people get less than 1 hour of vigorous exercise a day (or even a week). It doesn't matter how little you're spending, the body expects you're going need at least, say 1500 calories and for many people that's too many.

4. Something environmental. We're awash in so many new chemicals building up in our environments and bodies, and few have been studied for their long term effects. Maybe there's something in here that's throwing off internal signals or hormones.

>The fact it's not working means something's broke.

The brokenness usually comes from a diet high in overly processed food and refined sugar/starch, often coupled with little or no exercise.

Here's a paper relevant to the diet aspect:

Ultra-Processed Diets Cause Excess Calorie Intake and Weight Gain: An Inpatient Randomized Controlled Trial of Ad Libitum Food Intake:


I believe a good way to un-break things is gaining an awareness of where the calories are coming from, together with a. lot. of moderate exercise.

The above has worked well for me, but it's no quick fix, and wouldn't sell books, tv programmes, or speaking engagements.

'Eat less, move more' is overly simplistic, it's more about how you eat less and how you move more, to help the body's set point to shift back to a healthy level.

Calories in calories out could help if you could accurately measure them. I suspect that most people can’t. But you are right, internal mechanisms regulate both hunger and activity levels.

The point is that we shouldn't need to count calories.

> Calories in, calories out absolutely work.

Is this really true and known empirically? Could the body be better at accessing calories in some foods and not others?

Thought experiment: suppose I wrapped a small chocolate bar into airtight plastic, then I swallowed it. I have just swallowed 200 calories, but my body will access/process/burn 0% of it since it can't break down the plastic.

At least in this one (unrealistic) example, CICO is false.

> > Calories in, calories out absolutely work.

> Is this really true and known empirically?

If you are very careful about how you define “in” and “out”, to the point where it is nearly circular, and are concerned only about weight, not health, yes. It is still problematic in a number of ways, e.g.: if you just attack thr calories in side and have a relatively sedentary lifestyle, you will disproportionately lose lean body mass rather than fat, this not only is less than ideal as an end outcome, it also makes further weight loss more difficult because it reduces resting metabolic rate (and, therefore, minimum calories out) and makes it harder to do additional exercise to increase calories out.

It is likewis known empirically that, as actionable advice, its not particularly useful on its own besides those problems, for the same reason “don’t write bugs” is as advice on how to create correct software. Most serious weightoss advice incorporates CICO, but also adds layers on top dealing with the pragmatics of how to acheive that in a maintainable way (and usually also has at least some thought in how to do it in a way dealing with problems of naive CICO like those discussed above.)

It seems that nuts are harder to digest than we thought [0], and thus our bodies do not extract as much energy from them.

Also, composition of gut microbiota seems to have an effect on metabolism and obesity, at least in mice; that should not be surprising, given that gut microbiota "predigests" some nutrients for us. [1]

[0] https://thecounter.org/scientists-calorie-counts-usda-kind/

[1] https://www.ncbi.nlm.nih.gov/books/NBK154098/

Some foods have inaccessible calories. Most of what we call fiber has calories but the human gut can't get to it. I'm not 100% but I think if you can't access the calories then you don't count the calories.

CICO is shorthand for something complicated. There’s nuance, sure; but, most people could do with dropping the fork. Not always, but first measure of business should be to drop the fork and CICO until proven otherwise.

The body should be able to figure out how to not eat in excess.

It's absolutely true that if you count calories, you can manage the input such that you lose weight. But it is not a solution for the vast majority of humanity.

> The body should be able to figure out how to not eat in excess.

Why? Evolutionarily, we've had very little time where constant surplus was the norm, and mostly are adapted to situations where surpluses are rare and temporary abd shortages common.

Fighting that is hard.

Sure, our bodies might become good at that if we survive for another million years with first world standards of living as the norm. But they aren’t now, for good—evolutionary—reasons.

> Is this really true and known empirically? Could the body be better at accessing calories in some foods and not others?

Of course, 2000cal worth of HFCS is gonna have a different biological impact than 2000 cal worth of kale. CICO is a gross over-simplification.

This study appears to be specifically about people with Type 2 Diabetes. I wonder if the same holds true for healthy adults.

And it was only men, and it was a rather small sample size (32 total, split 12 morning and 20 afternoon).

I wonder if exercising at night has even better impacts. My jogs are usually sometime between 10pm-midnight. I recently mixed it up and went for a run in the late morning and it felt like I had lead feet...def impacted my body differently.

I cycle a moderate amount (~100km/week spread over 2-3 rides, typically in the 30-80km range), but drastically prefer starting early (generally pre-food, unless it's going to be a longer ~70km+ ride - in that case I know that I'll have to eat or I'll crash part way through). Feels far better.

I've also found that exercising in the morning, before eating, feels way better than at other times, especially in the evening.

But I've also found that my "feeling" of a session doesn't necessarily correlate with the performance. I wouldn't be surprised for other benefits to have a similar correlation.

However, as others have commented elsewhere, I think the issue for most people is not exercising at all, so for those cases the feeling you get while exercising absolutely matters. I'd say it's probably the most important thing, since if you feel like not exercising, you probably won't if it's not already ingrained in your routine.

Yes, good point - my subjective feeling of effort is often at odds with my measured performance with Strava.

And agreed on your second point too, I bike because I enjoy biking and it makes me feel better both physically and mentally. That I get good exercise out of it is a secondary benefit.

Guidelines | FAQ | Lists | API | Security | Legal | Apply to YC | Contact