Thin People Can Get Diabetes Too
We often associate diabetes with obesity. And for the most part this is true. Obesity is a risk factor for diabetes. Abdominal fat is an indicator of insulin resistance that is a precursor to diabetes.
However, it is possible for a person to be of normal weight and still have insulin resistance and diabetes. They may not have any abdominal fat and may even be thin.
There are two types of diabetes: Type 1 and Type 2. Type 1 diabetes is when the pancreas can not make enough insulin. Type 2 is when person is making enough insulin, but insulin is not effective in getting the glucose fuel into the cells. This is known as insulin resistance.
Insulin is a hormone that promotes the storage of fat. So for Type 1 diabetics where they do not make enough insulin, they certainly can be thin and still have diabetes. But Type 1 diabetes only accounts for roughly 10% of all diabetes.
It is the Type 2 diabetes that is often characterized by obesity. Type 2 is by far the most common form of diabetes (accounting for roughly 90%). Type 2 diabetes was formerly known as (and sometimes is still referred to as), "adult-onset diabetes". However with the diabetes epidemic, we are seeing children with Type 2 diabetes. So the term adult-onset may be slightly outdated.
Type 2 diabetes is when insulin ineffective in doing is job of shuttling glucose into the cells. Hence the pancreas has to pump out more and more insulin in its attempt to lower blood glucose (sugar) and try to move the glucose into the cells for energy. Since insulin also promotes fat, this condition results in added fat being produced.
However, even with Type 2 diabetes and insulin resistance, people can have it and still be thin. And many people have early stages of diabetes without even knowing it.
According to 2010 statistics, there were 27 million Americans who have clinical diabetes -- but only 75 percent of them was diagnosed. And there were 67 million with pre-diabetes -- only 10% of them was diagnosed. Some estimates say that by 2020, diabetes and obesity will affect one out of two Americans -- and 90% of them may not be diagnosed. [reference: Blood Sugar Solution page 7]
Article Impaired glucose tolerance in healthy men with low body weight depicts a study which found that people with low weight can have glucose intolerance. It says ...
"study demonstrates that not only obese but also healthy people with moderate underweight display glucose intolerance. "
In an article in MSNBC.com, Jeff O'Connell tells of his pre-diabetes even though he is not obese. In attempt to stave off diabetes, he eats a low-carb diet and exercise regularly alternating between cardio and weight training.
A study says that "even lean individual can be insulin resistant". We now know that insulin resistance is one pre-cursor to diabetes. One cause of insulin resistance is a fatty liver, or non-alcoholic fatty liver disease (NAFLD). You do not have to be fat to have a fatty liver. Thin people can have NAFLD just as obese people.
Page 153 of the book Primal Body, Primal Mind says it in black and white ...
"It is also possible to be thin and diabetic"
Article on Healthland.Time.com writes ...
"The elderly and people of Asian descent are more likely to be at normal weight when diagnosed, for example."
One study of 2625 individuals recently diagnosed with diabetes found that 12% were at normal weight.
Latent Autoimmune Diabetes in Adults
Some thin people with diabetes may actually have the autoimmune Type 1 form of diabetes rather than the type 2 form, even though their condition occurred during adulthood rather than occurring in childhood as Type 1 typically does. These cases are sometimes known as Latent Autoimmune Diabetes of Adults (LADA) -- or Diabetes Type 1.5. Think of it as a slower form of a Type 1 form of diabetes. In these cases, the patient is usually thin or of normal weight, although there are some who are overweight.
Diabetes.org has a good article describing Latent Autoimmune Diabetes of Adults in which it says that 10 percent of people with diabetes may have this form, making it more widespread than the type 1 form of diabetes.
On his website, Chris Kresser says that a quarter of the lean people diagnosed with Type II diabetes also produce the antibodies to GAD (glutamic acid decarboxylase-65) indicative of an autoimmune condition characterized by Type 1 diabetes.
Furthermore, he writes that stress can raise but sugar to unhealthy levels in even thin people...
"cortisol is capable of raising blood sugar to unhealthy levels even when a person is fasting. What that also means is that you can be lean, eat a perfect diet, and still have high blood sugar (and thus T2DM) if you suffer from chronic stress" 
Ultimately, diabetes is a metabolic disorder. Dr. Lustig says that 40% of thin people have metabolic disorders:
"Forty percent of those thin people, normal weight people, have those same chronic metabolic diseases." [from YouTube video]
Jenny Ruhl writes on her site ...
"Up to 20% of people diagnosed with Type 2 diabetes are not overweight. If you are one of them, it's worth doing some research to make sure that you don't, in fact, have one of the forms of what are often called "Type 1.5" diabetes, forms of diabetes that many doctors do not know about."
Asians more likely to become diabetic without becoming obese
Although Type 1 diabetes typically occurs before age 30, Sherri Shafer (in YouTube video on right) said that she has seen people in their 40's being diagnosised with Type 1. In video, she also says that people with normal body weight can still have Type 2 diabetes -- especially groups of Asian genetics.
There is genetic component and people with Asian ethnicity may more readily develop Type 2 diabetes (T2DM) with normal body weights than other group.
A study titled "Increased prevalence of insulin resistance and nonalcoholic fatty liver disease in Asian-Indian men" says ...
"In contrast to other ethnic groups, Eastern-Asians and Asian-Indians tend to develop T2DM without the same degree of generalized adiposity"
Time magazine has article that says that a growing number of diabetics in Asia are "well under weights traditionally matched with the disease" and that ...
"Skinny people with thick middles are particularly prone to developing Type II Diabetes"
The book Blood Sugar Solution also says similiarly ...
"people in this Asian population (who are uniquely susceptible to diabetes, even though they may not be obese) are increasingly affected as they adopt a more Western diet." [page 9]
and on page 174 ...
"certain ethnic groups such as Asians, Hispanics, Native Americans, Pacific Islanders, Inuit, Indians, and Middle Easterners have diabestity at much lower BMI's."
Many Reasons for Diabetes
The mechanism for diabetes is very complex, as shown by Chris Masterjohn's lecture below which suggests that glucose intolerance may be due to energy overload and that depletion of glutathione can result in insulin resistance.
In the book "The Obesity Paradox", it writes ...
"Most people wrongly assume that diabetes (and, for that matter, high cholesterol) is a "fat's person's" problem. This couldn't be further from the truth."
Article on Men's Health titled "Thin Man's Diabetes" tells of story of one "thin" person's high blood sugar.
Type I diabetes is when body can not produce enough insulin, resulting in high blood sugar. But it is possible that one can be slightly sub-clinical low on insulin (such as insulin insufficiency).
The book, The Blood Code, Dr. Richard Maurer writes that he sees low insulin in people who don't absorb enough calorie, over-exercise or work without enough recovery, and eating too low carb when there is no evidence of insulin resistance.
-  Even a thin person can get diabetes - MSNBC
-  Impaired glucose tolerance in healthy men with low body weight
-  Think Skinny People Don't Get Type 2 Diabetes? Think again
-  Dr. Bernstein's Diabetes Solution - book
-  Fatty liver: a novel component of the metabolic syndrome
-  Latent Autoimmune Diabetes - Wikipedia