I am amazed naturally skinny people even exist.

Think about it. For most of human history we’ve lived on the edge of starvation. The only plentiful thing was famine, especially in winter. Our Stone Age ancestors spent all summer hunting and gathering everything they could shovel into their root and berry holes in an attempt to add enough body fat to survive the coming lean times.

Natural selection favored those who could easily gain and store fat, and wouldn’t lose it quickly. People without these genetic tendencies got Darwined long ago. If you’re alive today, it’s because your long lost ancestors were able to store fat for the times when the body had nothing to eat except the stuff you’d packed around your midsection.

Hopefully that gives you some context about living in an era where we complain if the drive-through window is closed.

We’re inundated with rapid fat loss scams. How many times have you see an ad or article proclaim: “Lose [insert ridiculously high number] pounds of fat in only [insert stupidly short number] of days.”

And those “amazing” before and after photos? Yeah, check this video out.

I’m not saying physical transformations aren’t possible – they are. I know because I’ve done it. But they are neither quick nor easy. The fact is, if you’re carrying around extra poundage it’s at least in part because you’re genetically programmed to. When you try to lose it your body will fight you. In some ways, your body still thinks it’s the Stone Age. It doesn’t know there is a grocery store just down the road.

The more fat you lose, the slower your metabolism gets. What’s more, if you’re upping activity levels to achieve fat loss goals, know that this makes your body more efficient at movement. Yes, you burn lots of calories while active, but while at rest it begins to burn fewer calories. There is also the fact as your body becomes lighter you simply have less to carry around with you on everyday tasks, which will also burn fewer calories.

For me, in that “before” picture I weighed well over 200. I lost over 50 pounds of fat and gained close to 25 pounds of muscle. Even for mundane things like climbing stairs or walking or doing housework it’s like I un-shouldered about a 30-pound backpack of blubber. It makes moving around a lot easier, and because it’s easier, it burns less calories. And that extra 25 pounds of muscle, while helpful, isn’t boosting my metabolism much. That’s a myth.

Add to this the fact that when fat stores get low, your body begins to hate to you.

This study in the Journal of Theoretical Biology shows that the less body fat you have, the less it will choose to burn. When you begin to get lean enough that you can almost see your abs, fat loss slows to a crawl, and if you push the caloric deficits anyway, then you’re going to lose fat free mass instead (that means losing muscle, which is bad). That period of time between “a hint of abdominal definition” and “hey, my abs are popping” can be maddeningly long.

If you’re 20 pounds away from six-pack abs, the first ten won’t be that hard to lose. Then next five will suck. The final five will make you want to drop kick a kitten into a wood chipper.

Let’s get one thing straight: For the vast majority of people the journey to six-pack abs is long and tortuous. Don’t listen to just me. Listen to these six guys with six-packs who I interviewed about how hard it is. Hell, as you can see from the photo on my website I got to the “four-pack” stage and decided that was good enough. Mind you, I’m in my 40s; most guys in my age group are working towards their first heart attack.

There is no quick, and there is no easy. This is a hard slog of lots of intense exercise and dietary deprivation. Not starvation, but junk food and booze need to be dramatically cut, and you may find you are becoming obsessive in regards to caloric balance.

And then, finally, when you achieve your desired abdominal definition you must sustain the lifestyle that got you there in order to sustain the abs.

So why would you want to do this? Sometimes I ask myself that question. According to my “research,” you probably won’t get laid more. Hell, it actually removes some padding down there and may result in complaints. Unless you live near a beach it’s not like there are lots of opportunities to show them off, and you want to know something? Showing them off gets old. At first you may notice admiring glances here and there, but then you stop noticing them.

My wife almost never says anything about my abs anymore. They’re just kind of there.

So why do I strive to sustain mine? One reason: I like the way they look. Me. I get a kick out of seeing them in the mirror.

Yeah, I know that’s stupid and shallow, but it’s what pushes me. In 2015 they went away because of illnesses, injuries and some other general life suckage, and I missed them. Now, after a few months of hard work, they’re almost back and I’m excited. Maybe that’s not the most mature thing to be excited about; I don’t care.

If you decide that you’re willing to do what it takes to attain and sustain abdominal definition, then you need to find your why. And most important, you must be patient.

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James S. Fell is an internationally syndicated fitness columnist for the Chicago Tribune and author of Lose it Right: A Brutally Honest 3-Stage Program to Help You Get Fit and Lose Weight Without Losing Your Mind, published by Random House Canada. He also interviews celebrities about their fitness stories for the Los Angeles Times, and is head fitness columnist for AskMen.com and a regular contributor to Men’s Health.