A stationary bike at a steady 20mph pace is about 500 calories in 30 minutes. That's really significant. An hour will erase about a third of a normal person's diet.

When I used to do heavy training (long distance running, weight training) I would eat close to 8k calories a day and I was in fantastic shape. Eating more was necessary to survive, given how much energy I was expending.

That assumes a “normal person” will not compensate for the effort with a snack.

A “reward” pint of ice cream will re-add more calories than the hour of cycling. A “standard serving” will nearly match your half hour.

And that’s an hour at 20mph, which really isn’t in any way the norm.

You're also assuming the same normal person will not compensate for their healthy lunch with a snack.

Measuring stationary bike workouts in terms of mph is kind of meaningless. What actually matters is the measured power output based on the resistance setting.

It took me about three months to get up to that speed, cycling every other day. I started out doing 10 miles, at 10mph.

Three months isn't all that long for an exercise program.

There are certainly plenty of trained cyclists who can maintain that power output, but I've never seen anyone reach that level after only 3 months. If you really did that then you're an extreme genetic outlier with an unusually fast training response.

I did a lot of cycling in my 20s and while I'm at least a decade out of shape I'm sure I'm relying a lot on past training.

Absolute heart rate doesn't tell us much about calorie consumption because there's a huge variation between individuals. If we know the athlete's size, sex, and threshold heart rate then we can start to make some kind of estimate. But to get an accurate number it really takes a properly calibrated power meter (or more complex lab tests involving exhaled gas measurement).

What is the actual power output in watts? Has it been properly calibrated? If not then you're just fooling yourself.

These statements are rather extreme and seem impossible to support. Energy output per mile with real world cycling has enormous variance as well. Why so much concern for precision regarding one and not the other?

I don't think there's much point in continuing here.

You can get an accurate calculation of real world cycling calories with a power meter. Everyone's cycling efficiency in terms of power output per calorie burned falls within a fairly narrow range so converting from time and watts to calories is simple. A good power meter accurate to within a couple percent can be added to any bike for about $700.

Smart trainers like a Tacx Neo or Wahoo Kickr also have accurate power meters built in. Those are substantially different from typical stationary bikes.

I understand the translation between power and mph is somewhat approximated, but I think you could be more generous. It's not unreasonable to make this kind of approximation and the numbers aren't meaningless.

I cycle on and off for ~8 years (35yo) and going at 20mph in the real world for an hour or more became possible only after a few years for me.

As a point of comparison, an average size man would have to run at a speed of at least 11 mph (18 km/h) in order to burn that many calories in 30 minutes. Not impossible, but well beyond what most of us can manage.

It is also something at most a tiny minority of the obese population can do.

Fats are the secret to obesity, hands down. I have a remarkably small appetite and I can easily down 1000 calories of ice cream in a single sitting (a single pint of Ben and Jerry's. You can row like crazy for 30 minutes, but if you have two extra candy bars, it's meaningless.

Yes, our bodies are built to take in more calories than we can burn (thankfully!), but if you keep your eating habits constant the exercise will make a huge difference.

Pretty sure most people shouldn't be eating 3000 calories/day.

The thing is, the 300 calories from rowing shouldn't be compared to the absolute calorific requirement (say 2500 calories) but the surplus. So Maybe I'm overweight because I need 2500 and I eat 3000. Thats 500 too much, but take out 300 and that's 60% of what I need to at least reach equilibrium. It makes a huge difference to how much I need to sacrifice out of my diet.

"You can't exercise your way out of a bad diet" - literally not true for a fuckton of endurance-sport athletes for whom the challenge is eating enough calories.

It's 100% true for people who think exercising for 30 min means license to eat whatever.

> So a good diet: takes less time than exercise, reduces calories more, and can save money

Yes, but endurance exercise over an hour or two brings its own advantages health-wise.

The real takeaway is that there are no absolutes.

While I do agree with you that sustained, high level activity requires and burns more calories, I think that the advice coming out of there, exercise is less efficient than diet for weight loss, is going to absolutely be true for the majority of gym goers who quite frankly are phoning it in whenever they work out.

Like, for example, an olympic swimmer may eat 5000-10,000 calories in a day, but they are spending around 4-6 hours a day in a cold pool training at a world class level (body needs to keep warm somehow regardless of effort.) But a normal person may only swim for 20 minutes at a much gentler pace. This person should still be eating in line with calorie guidelines and macros for age/sex.

The reality is that diet needs to be flexible based on results. Not losing weight? Eat fewer carbs or calories. Feeling tired and worn out? Eat more or exercise less based on your physique and goals.

I don't know how things are for anyone else, but it worked for me, shrug.

Attempts to loose weight by diet only all failed. To make it worst, there is also aspect of most common diet advice being plain wrong. It focuses on calories too much. It completely ignores what your body needs, so you end up in nutritional deficiency - this kind or that kind. And that will affect a lot and eventually you will stop diet and start to feel so much better and healthier after stopping it.

The calorie stuff is from both oxygen and deuterated water studies. You burn the same amount of calories and your system just shunts them around. The science on this is one of the few things in nutrition that is quite solid.

This has the effect, for example, that if you exercise a lot, this actually suppresses your immune system making you more likely to get sick.

Are you sure? 2000 kcal in 3 hours is 770 watts of power output.

Edit: Wikipedia [0] says "During a bicycle race, an elite cyclist can produce close to 400 watts of mechanical power over an hour and in short bursts over double that - 1000 to 1100 watts; modern racing bicycles have greater than 95% mechanical efficiency. An adult of good fitness is more likely to average between 50 and 150 watts for an hour of vigorous exercise."

[0] - https://en.wikipedia.org/wiki/Human_power

I'm not, because the parent poster explicitly said "That's not based on made-up calories but actual work from a power meter on the bike."

Which seems absurd, hence my comment.

Hello old friend, we meet again.

The article is taking this one step further though and saying those 300 calories burned by exercise are simply conserved elsewhere throughout the day automatically by your body.

The claim then is that if you exercise and burn 300 calories, but eat an extra 300 to offset it you won't end up at a neutral state and instead will gain weight as if you hadn't exercised at all.

Rough math: 3 * 300 * 4 = 3600 calories surplus/month. A pound of adipose tissue has ~3500 calories IIRC. So you're now gaining a pound of fat a month, and you're not even indulging yourself, really.

In reality, physical activity and diet aren't so steady, so some months you maintain weight, some you lose, and some you gain a lot. But over time it averages out, and you've put on 12lbs in a year.