Fasting on Yom Kippur — Part 2: A Low-Carb Diet Preceding a Fast

BS"D

In this post:

• You're Late in the Game
• What About Drinking the Day Before?
• What People Tell Me
• I Am Not Telling You to Change How You Eat
• The Locked Door
• Why They Are Not Thirsty
• It Is Not One Change
• Ketosis Is Not DKA
• If You Are Starting Now
• And This Goes Double for Us

You're Late in the Game

A common dialogue in our home. In the last few hours before a fast, one of my children asks me what he can do to make the fast easier.

My answer is always the same. You're late in the game.

For the water, you should have started this morning. For everything else, you should have asked me weeks ago.

Then comes the second question, and it is a better one. So what could I have done weeks ago? At least I will know for next time.

That is the question this post answers.

And there is good news this year, because Yom Kippur is still about three weeks away. Three weeks is not a lot. It is also not nothing. Ask me again in two weeks and my answer will be a different one.

What About Drinking the Day Before?

The advice going around every year is to make sure you drink plenty the day before the fast. That is right, and I am not telling anybody to drink less. But how you drink it over that day makes a difference most people do not know about.

Let's start with what the last hour does not do. When you drink a large amount at once, your body does not keep most of it. Your kidneys notice that the blood has become watery, and they send the extra right back out, usually within an hour or two. You cannot fill a tank that has no room in it. So the man who sits down before the fast and drinks four cups of water is mostly making a trip to the bathroom.

Take those same four cups and sip them through the whole day, a little at a time, and your body keeps far more of it. The blood never gets watery, so the kidneys never dump anything. The amount was identical. What it did for you was not.

That is the one thing in this post you can still do on the day itself. Everything else needed weeks.

What People Tell Me

Over the years people have told me something I keep coming back to, and I have felt it myself.

A person who has been eating low carb in the weeks leading up to a fast has an easier fast than a person who was eating the way he usually eats.

Most of the people who have told me this have Type 2 diabetes, and their situation is not the same as ours. But I have experienced it myself, and the reasons behind it — which are the rest of this post — apply to every person who fasts. They apply to us most of all, and I will come back to that at the end.

One detail comes up again and again, and it is the detail that made me start taking this seriously. They tell me that during the fast they are not thirsty. Not less thirsty. Not thirsty at all.

I Am Not Telling You to Change How You Eat

I am not telling anybody with Type 1 to switch over to a low-carb diet. Making that change with Type 1 is a real change. Your carb ratios move. Your basal moves. Your correction factor moves. It needs a doctor, it needs proper instruction, and it needs somebody watching your numbers while you settle in. It is not something to start because you read a post.

So who am I talking to?

I am talking to the person who has already done this before. You know how it works for you. You know what your numbers do. You know how to adjust. You have simply never thought about the calendar.

The Locked Door

Your body can run on three different fuels. It can run on glucose — sugar. It can run on fat. And there is a third one, which you have certainly heard of, but probably never thought of as fuel at all. I will come to it in a minute.

Insulin has a job, and the job is not only to bring your sugar down. Insulin's job is to store. When insulin is up, the body is in storing mode. Put the sugar away, put the fat away, hold on to what you have.

And here is the part that matters for a fast. As long as insulin is up, your fat stays locked away. Your body is carrying it, but it cannot spend it. Insulin is holding the door closed.

So picture a person who eats plenty of carbohydrates through the day. His insulin is up for most of the day. He is running on sugar, and his fat is sitting behind a locked door.

Now the fast begins. The sugar in his blood gets used up. The sugar stored in his liver gets used up. And then he needs something else to burn — but his door is still closed, and it takes time to open it.

Those are the hours he feels terrible.

Now the brain.

The brain cannot burn fat. Not a little bit. Not at all. Fat cannot get into the brain. The brain has exactly two fuels available to it: sugar, and ketones. That is the whole list.

And there is the third fuel I mentioned. Ketones. You know the word from test strips and sick days, and we will come back to that. But this is what ketones actually are: your body's other fuel, and one of only two the brain can use at all.

Think about what that means on a fast day. The headache. The fog. Not being able to daven with kavanah. Those are not your muscles complaining. Those are all coming from your head. That is your brain sitting there with the sugar running out, waiting for its second fuel to arrive.

And ketones are made out of fat. So your brain is waiting on a door that is locked somewhere else in your body.

Now the other one. This person has been eating low carb for weeks. The insulin has been low the whole time. The door has been open for weeks. The body is already burning fat, the liver is already making ketones, and the brain is already using them.

When the fast starts, nothing has to change. The change was made weeks ago.

Why They Are Not Thirsty

Insulin does something else besides storing fat. It tells your kidneys to hold on to salt. And wherever salt goes, water follows. So a person whose insulin is up most of the day is in holding-on mode for salt and water too.

Now take that person into a fast. His insulin comes down. His kidneys let the salt go, and water goes out along with it — and it is happening during the fast, when he cannot drink anything to replace it.

The person who has been eating low carb for weeks already went through that adjustment. His kidneys let that salt and water go a long time ago, and he settled at a new level. There is nothing left for him to let go of on the fast day. He walks in balanced, and he stays balanced.

That is why they tell me they are not thirsty. They are not imagining it. They really are in better shape than the person sitting next to them.

It Is Not One Change

I have been describing this as though it were one switch, and it is more than that. Several different parts of the body have to change, and every one of them takes time.

• Your body has to get used to unlocking fat instead of reaching for sugar. Weeks.
• Your liver has to get practiced at making ketones. Weeks.
• Your brain has to build up the doors that let ketones in. Weeks.
• Your liver has to get practiced at making its own sugar, once the stored sugar runs out. Weeks.
• Your kidneys have to settle into holding less salt and water. A week or two.

Not one of those things happens on the fast day. So there are only two possibilities. Either your body did them in the weeks before, and by the time the fast starts there is nothing left to do. Or it is doing them while you fast.

That is where the misery lives. Not in the fasting itself. In the hours it takes your body to switch from running on one fuel to running on another. The crossing is what feels horrible.

That is why my answer to the man who asks me the day before is that he is late. Not because I do not want to help him. Because there is nothing anybody can do in one day that these weeks would have done for him.

Ketosis Is Not DKA

I have used the word ketones a number of times now, and I know what happens when a person with Type 1 hears that word. So, let's clarify it.

Ketones are normal. Every person who fasts makes ketones. Your body has been doing this every night of your life while you sleep (minuscule amounts of ketones), and on every fast day you have ever had. It is your body's other fuel, doing exactly what it was built to do.

DKA is something else. In DKA the ketones climb many times higher, the blood itself turns acid, and the person becomes sick.

What holds the two apart is insulin. Ketones stay in the normal, safe range as long as there is enough insulin in the body.

There is more to say here, and it deserves a post of its own — particularly for a person who is already in ketosis walking into a fast, because his situation is not the same as everybody else's. B'ezras Hashem I will write it.

If You Are Starting Now

Yom Kippur is about three weeks away.

Three weeks is enough to feel a difference. It is not enough to land where a person who has been living this way all year lands. If I promised you more than that and your fast was still hard, you would decide the whole thing was nonsense.

One thing to expect. Your doses will not settle in a day. They will keep moving over these three weeks while your body adjusts, so you will still be watching them the week of Yom Kippur.

And This Goes Double for Us

Everything in this post is true for anybody who fasts. Every person has a liver that locks the fat away when insulin is up, a brain that can only burn sugar or ketones, and kidneys that hold on to salt. Any person alive would have an easier fast for having eaten low carb in the weeks before it.

It is more true for a person with Type 2, whose insulin runs high all day — which is no coincidence, since that is who has been telling me about it.

And it is most true for us.

In a person without diabetes, the insulin is made by the pancreas and goes to the liver first, and the liver removes half or more of it before it even reaches the rest of the body. Our insulin does not travel that road. It goes in under the skin and straight out into the body, so the very same amount leaves about twice as much insulin circulating through our muscle and our fat. I went through this in the Friday Feedback Forum on weight gain.

Now put that together with what I described earlier. The door that insulin holds closed on your fat is in the fat tissue itself. And the fat tissue is exactly where all that extra insulin is sitting.

So the door is locked tighter for us than it is for anybody else at the table. Which also means that opening it does more for us than it does for them.

What helps everybody helps us more.

— Rabbi Hirsch Meisels

P.S. If you have done this — kept a low-carb diet in the weeks before a fast — I would like to hear about it. How the fast went. Tell me about the years you did not do it, and about the year you did, and what the difference was. What was different about the afternoon. What was different about how you felt when you broke the fast. That comparison, from one person about himself, is worth more to me than any general answer, and it is what will make the next one of these posts a better one.