Most articles describing the benefits of intermittent fasting and ketogenic diets focus on  weight loss and, to a lesser extent, greater mental clarity. (Healthier and sharper? That's something every entrepreneur can use.)  

That's why keto diets and intermittent fasting are hot. They're a great way to burn more fat, one of the goals of most weight loss plans. (While a keto diet is different from intermittent fasting, most people that follow a keto diet also employ some form of intermittent fasting in order to enter ketosis more quickly.)

But you don't have to lose weight: The combination of a keto diet and intermittent fasting is also a great way to simply shift your muscle to fat ratio toward a greater percentage of muscle

Just ask Washington Redskins quarterback Alex Smith. After the 2016 season, Smith went all-in on a keto diet and maintained the same body weight... but his body fat percentage shrank from an already lean 10 percent to just 4 percent over the course of a few months.

Same weight -- but less fat and more muscle.

That's because intermittent fasting is not a diet (although you can follow an intermittent fasting schedule in conjunction with a calorie reduction plan). Intermittent fasting is just a different way of eating: Intermittent fasting is all about when you eat, not what you eat.

In Smith's case, he only eats within the hours of noon and 8 p.m. He's a believer in bulletproof coffee (coffee mixed with butter and/or oil to increase the fat content; here's a great recipe). He eats clean -- chicken, fish, proteins, low-carb vegetables, healthy fats -- but he doesn't count calories.

And then for the next 16 hours he fasts (hence "intermittent" fasting)... and then starts the process all over again the next day.

As Smith says, "It's helped me focus these last few years ... I feel really good practicing. I feel light, my arm feels great, I feel like I have far less inflammation because of it. And I certainly leaned up quick."

So why do keto diets and intermittent fasting work?

The Science of Ketogenic Diets

Generally speaking, with a ketogenic diet you try to consume less than 50 net carbs per day while maintaining a 4:1 ratio of fat to protein and carbs. The goal is to "train" your body to burn fat for energy instead of carbohydrates.

Why? For one thing, fat is the most efficient energy source. Two, starving your body of carbs is beneficial since carbs are the easiest form of calories to convert to fat. So in effect you double-dip: You burn more fat... and you create less fat.

Of course a 4:1 ratio of fat to protein/carbs is pretty tough to maintain for most people. That's why many people follow a "modified" keto diet, shifting the ratio to something more along the lines of 3:1 and occasionally even 2:1. While that is outside the strict definition of a keto diet, which means you would maintain a low to moderate state of ketosis, you'll still see benefits.

Especially when you add intermittent fasting to the mix.

The Science of Intermittent Fasting

Think of your body as being in two states: the "fed" state and the "fasted" state.

The fed state occurs when you are digesting and processing food. Start eating, and your body shifts into the fed state. Even after you've finished eating you stay in the fed state for roughly three to five hours (depending on what you ate, how often you you eat, your metabolic rate, and other factors.)

When you're in the fed state your insulin levels naturally increase, and when your insulin levels are high you typically don't burn fat for energy -- your body doesn't need to tap into its fat stores because what you're eating gives it plenty to work with.

After somewhere between three and five hours your body stops processing its last meal. There's nothing left to absorb and insulin levels naturally decrease. After somewhere between eight and 12 hours after that last meal, your body starts to burn stored fat. (Why don't you start burning fat sooner, you ask? Biology is sometimes a pain in the ass; it's like our bodies will do anything to hang on to fat. )

In short, when you're in the fed state your body doesn't need to burn fat; it's like the door to the fat warehouse is locked. When you're in the fasted state, the door to the fat warehouse swings open.

But it takes eight to 12 hours of not eating to get into the fasted state. Start your day with breakfast at 7 a.m., eat throughout the day, and have a 9 p.m. snack... and you almost never go into a fasted state.

Fast for 16 hours, and you do.

And that's how, over time, you can lose a few percentage points of body fat even if you don't change your exercise routine and don't change what you eat. Keep all the other variables constant and intermittent fasting will cause you to lose fat.

Science says so; in one study, after eight weeks participants who followed an intermittent fasting eating schedule lost 3.5 pounds of fat while those who similarly exercised and took in the same total calories did not. In another study, participants reduced their waist circumference by 4 to 7 percent. Other studies have shown that fasting can reduce the risk of cardiovascular disease and cancer.

Plus, who can ignore Jackman science: To play Wolverine, Hugh Jackman followed an intermittent fasting eating regimen and put on 25 to 30 pounds of muscle while also leaning out.

Yep: Intermittent fasting works.

Want to Channel Your Inner Alex Smith?

The beauty of intermittent fasting is that there really is just one rule: Eat for 8 hours; don't eat for 16 hours. (Some people choose to fast for 18 hours. Try that if you want... but that's a long time to go without eating.)

When you decide to start eating is up to you. What you eat during that time frame is up to you.

Figure out what works best for your schedule and your lifestyle.

Most people wait a while after they wake up to start eating; when I've followed an intermittent fasting plan it was easier to hold off for a few hours in the morning than it was to go, say, from 3 or 4 p.m. until bedtime without eating. Plus, if you work out in the morning before you eat, you get to double-dip on fat burning, since your body will use even more of your stored fat for energy.

For most people, that means eating fewer times during the day; before I started intermittent fasting, I was eating six or seven small meals each day. If you're not trying to lose weight, you may have to eat a little more than normal at each meal. (If you are trying to lose weight, intermittent fasting may help you consume fewer calories simply because your "eating window" is smaller. Win-win.) 

At first it won't be easy to switch over to a new eating regimen, so consider easing into it. Start out on a M-W-F plan, following an intermittent fasting and keto diet on Monday, Wednesday, and Friday, and eat normally the other days. After a couple of weeks, add in another day. And then another....

And keep in mind you don't have to go all-in on. Dick Costolo, ex-Twitter CEO, takes Sundays off. Other people take a day off every two weeks or so. Some never go past a M-W-F schedule. Research shows that some of the benefits of intermittent fasting and keto diets still result from a more limited approach.

But whatever you do, create a plan and stick to that plan. Don't only fast when you feel like it. Don't only eat keto (or even just low carb) when you feel like it. Make a plan and follow your plan. And if you fall off the eating plan wagon one day, just jump back on the next day.

If you do your best but can "only" stick to your plan 90 percent of the time, don't beat yourself up. 90 percent is great -- and so are the benefits you'll see.

Remember, life isn't all or nothing. Even diets.