No. This is a common misconception and is not true.
From an evolutionary perspective, we were designed as Stone Age hunter-gatherers who would frequently go for extended periods of time without food and even water. Because of this, nature has designed us with beautifully engineered biological mechanisms to prevent our blood sugar from dropping below a required level if we don’t get enough to eat.
As a matter of fact, we can literally produce all the sugar we need by converting stored fat or protein into glucose (blood sugar).
If we were so unfortunate to have to go without food for a week (say by being lost in the woods), our blood sugar would remain perfectly normal. Now we might feel extremely hungry and our stomachs might grumble but whatever symptoms we might experience would not be because of low blood sugar.
An example of this is unfortunately with us every day. There are many impoverished areas of the world where countless individuals will frequently not eat for extended periods of time. Yet they can endure this without the ill consequence of hypoglycemia (low blood sugar).
So what causes the symptoms that are so often associated with ‘low blood sugar’ and why do they get better when we eat?
These symptoms are often caused by low-grade nausea from acid building up in the stomach throughout the day (due to autonomic dysfunction), and ingestion of food acts as a mild antacid as well as a stimulant for the stomach to empty some of its acidic contents. Both of these things reduce the acid burden within the stomach and cause or symptoms to go away.
So when we are feeling weak or shaky in the afternoon and it seems to get better with food, remember you probably just need to reach for an antacid (like Tums) instead of a snack.