A grumbling stomach and slight abdominal discomfort ("hunger pangs") are the most common first signs of hungry. Go without eating for a bit longer, and you may start feeling grumpy, shaky, and become unable to concentrate.
It's common enough, that's for sure — type "when I'm hungry I" into Google, and "feel nauseous" automatically emerges as a suggestion. While that statement is hardly worth as much as a scientific study probing into the percentages of people who feel sick to their stomach when they're hungry, the fact remains that Google doesn't offer those autofill suggestions if only two or three people a month use that search term.
Hoping to find out more, I informally surveyed some of my friends. Sure enough, they, too, are familiar with the phenomenon. A friend with hypoglycemia told me that she experiences nausea when hungry, while another, who never had her blood sugar levels checked, feels nauseous while hungry too sometimes and attributes it to PMS. Yet another takes nausea while hungry as a sign that he's ingesting too many highly processed carbs and needs to lay off the junk food. They all, in other words, have their own theories about why they feel a bit queasy when they're hungry. Are they right?
Let's investigate that!
Could Your Nausea While Hungry Be A Sign Of Hypoglycemia?
The most common symptoms of mild to moderate hypoglycemia — or blood glucose levels that are lower than they should be — are sweating, shakiness, heart palpitations, and slight anxiety, along with fatigue, headache, and blurred vision. Guess what two other symptoms characterize low blood glucose levels? Yup; hunger and nausea. [1, 2]
Hypoglycemia is strongly associated with diabetes, and diabetics who are using insulin or diabetes pills called sulfonylureas and meglitinides are particularly likely to experience low blood glucose levels. Skipping meals, not getting enough carbs, drinking too much alcohol, and a sudden increase in physical activity can also lead to hypoglycemia in diabetics. 
While hypoglycemia is actually pretty rare in non-diabetics, several serious medical conditions are also associated with low blood sugar levels. They include kidney, liver and heart failure, insulin or insulin receptor antibodies, traumatic injuries, or deficiencies in certain critical hormones. 
Please make sure you eat regular and varied meals, and meet your caloric needs. Seeing a doctor certainly won't do you any harm, however.
Hunger And Nausea: Could A Peptic Ulcer Be To Blame?
A peptic ulcer is a sore in the lining of the stomach or the first portion of the small intestine. It can occur when the lining of either of these two parts of your anatomy starts to break down. Risk factors for a peptic ulcer include drinking too much, smoking, receiving radiation therapy, and overusing NSAID pain killers or Aspirin. 
Not everyone with a peptic ulcer will have obvious symptoms, but those who do may experience pain, an unusual feeling of satiety, darkened stools, fatigue, and weight loss. Hunger and nausea are other symptoms of a peptic ulcer. As one paper points out: "Many duodenal ulcer patients report that the pain occurs when the stomach is empty or is relieved by food, and follows a pattern of relatively long periods of freedom from symptoms between recurrences." 
Nauseous While Hungry During Pregnancy?
The vast majority of pregnant women — an estimated 90 percent — experience some form of nausea or vomiting. You may have heard that certain foods or smells can trigger episodes of morning sickness, but is it also possible to experience morning sickness as the result of an empty stomach?
You bet. Research suggests that expectant moms who are dealing with morning sickness from hell are best off making sure their stomach is never empty. If you're pregnant and feel nauseous whenever you haven't eaten in a while, consume small meals every few hours, and snack on high-protein foods, such as a handful of nuts, between meals. Are you in your first trimester and taking a prenatal supplement that contains iron? This, too, may be a cause of your nausea while hungry. You may want to consider switching to folic-acid-only supplements and getting your iron exclusively through your diet — especially if you are not anemic. 
Medications And Nausea While Hungry
If you're using antibiotics (especially Erythromycin) , non-steroidal anti-inflammatory drugs such as ibuprofen, naproxen, or ketoprofen , or even something as simple as multivitamin supplements , you should be very careful to follow the instructions provided on your medication's package insert.
Why Else Could You Feel Nauseous On An Empty Stomach?
Interested in finding out why people told me they feel nauseous on an empty stomach when they're PMS-ing or eating a carb-filled junk food diet, I turned to one of SteadyHealth's "in-house" physicians, Dr Sasa Milosevic.
He told me it's fairly logical to feel sick to your (empty) stomach while on a very high-carb diet, because:
A meal very high in carbs induces the release of more insulin than after a usual meal. Insulin helps the carbs to enter the muscle cells and fat cells more quickly. If the time between meals is long (which it usually is with these types of diets), the consequence is a fast drop in blood glucose levels, hence – hypoglycemia, which may then cause nausea.
The moral of the story is, of course, that exploring healthier foods doesn't just confer long-term health benefits but also short-term advantages. If you're feeling sick when hungry on a high-carb diet, your body's telling you you're not feeding it the foods it really needs to stay healthy.
What about PMS, then? Dr Milosevic says:
I suppose you can put it in the context of appetite changes. Appetite changes (an increased or decreased appetite) during PMS can cause changes in the amount of food intake that the gastrointestinal system is not accustomed to. And a sudden increase or decrease in food intake can cause nausea.
Another possible cause of nausea on an empty stomach is stress. It's pretty common to experience nausea or abdominal pain when you're under immense amounts of stress, and doctors are often unable to find a physical cause of this pain and nausea.  It may not be hunger that's making you sick, but stress.
Finally, does your child complain of nausea on an empty stomach? While it's always good to mention this to your pediatrician the next time you see them, it's quite possible that "I feel sick when I get hungry" is simply your kid's way of describing the grumbling stomach and hunger pangs typically associated with hunger.