Runners & Fuel Sources

The Shakes Are a Good Sign

That lightheaded, shaky, sick feeling when you're hungry? Your body is about to burn fat.

Here's something most people don't know: almost every adult in the United States could go two full weeks without eating and not experience a single devastating side effect.

Uncomfortable? Absolutely. Stomach pains, hunger pangs, irritability — yes to all of it. But devastating? No. The man in the 1976 fasting study said the first two to three months were the hardest. After that, it became routine. He adjusted to the new normal and kept going for another ten months beyond that.

I'm not recommending a two-week fast. But understanding that the body is far more resilient than we give it credit for is an important starting point — because it changes how you interpret what happens when you cut calories and start feeling hungry.

What's Actually Happening When You Get the Shakes

You know the feeling. Blood sugar drops. Heart rate climbs. You break out in a light sweat, feel a little lightheaded, start shaking. It's unpleasant. A lot of people panic and reach for food immediately.

Here's what I tell my patients: that feeling is a signal, not an emergency. What it means is that your blood sugar has bottomed out — you've used up your available glucose. And when you have no blood sugar left, there's only one fuel source left to burn.

Fat.

That shaky, uncomfortable feeling is your body transitioning into fat-burning mode. It's not a warning that something is going wrong. It's a sign that the process is working.

What to Do When It Hits

When you feel it coming — the shakiness, the lightheadedness, the nausea — get up and take a brisk walk. Push your heart rate up a little. Don't reach for food.

I know that sounds backwards. But here's why it works.

What Marathon Runners Can Teach You About Fat

A marathon is 26 miles. At mile five or six, a runner's blood sugar is gone. They only carry so much glucose, and sustained effort at that level depletes it fast.

But you don't see marathon runners at mile seven stopping on the side of the road, shaking, unable to go on. Their bodies made the switch — from glucose to fat — and they kept running. Miles seven through twenty-six are powered almost entirely by stored fat.

The difference between a runner and someone sitting on the couch when blood sugar drops is activity.

When you're running, your body anticipates the demand. The moment you start moving, adrenaline begins to release. By the time you run out of glucose, the fat-burning machinery is already warmed up and ready. The transition is smooth because the body was prepared for it.

When you're sedentary and blood sugar drifts down, your body releases adrenaline too — but as a distress signal rather than a prepared response. It's dispatching norepinephrine and epinephrine to break down free fatty acids and keep things running. That's the shaky, sweaty, anxious feeling. The chemistry is similar. The experience is very different.

Getting up and moving when that feeling hits does two things: it tells your body this is intentional, and it accelerates the switch to fat metabolism. Walk briskly, push through it, and within a few minutes the feeling passes — because now you're burning fat.

The Bottom Line

Hunger is uncomfortable. The shakes are uncomfortable. But discomfort is not the same as danger. Your body has extensive reserves and knows exactly how to use them. The transition from burning sugar to burning fat is a normal biological process — one that every marathoner relies on without a second thought.

Learn to recognize that feeling for what it is, and it stops being something to fear.

If you want help understanding your body's signals and building a plan around them, that's exactly what we do.

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