The primary chemical missing in a diabetic patient is insulin, a hormone produced by the pancreas that allows your cells to absorb sugar from the bloodstream and use it for energy. Without enough insulin, sugar builds up in the blood while cells starve for fuel. But insulin isn’t the only chemical thrown off balance. Diabetes disrupts an entire network of hormones, and understanding which ones are affected helps explain why the condition causes so many different problems.
How Insulin Works in a Healthy Body
Your pancreas contains clusters of specialized cells called beta cells. When you eat and your blood sugar rises, beta cells release insulin into the bloodstream. Think of insulin as a key that unlocks your cells so sugar can move inside. Once sugar enters the cells, your blood sugar level drops back to normal. This cycle happens continuously throughout the day, keeping blood sugar within a tight range.
Insulin also tells your liver to stop releasing stored sugar and signals fat cells to hold onto their fat reserves. When insulin is missing or not working properly, both of those brakes come off, flooding the blood with even more sugar and releasing fats that can cause further damage.
Type 1: Near-Total Insulin Loss
In Type 1 diabetes, the immune system mistakenly attacks and destroys the insulin-producing beta cells in the pancreas. This eventually results in a total lack of natural insulin. By the time symptoms appear, roughly 50% or more of beta cell function has already been lost. A blood test called C-peptide, which measures how much insulin the body is still making, drops below 0.2 nmol/L in Type 1 patients, confirming near-complete shutdown of production.
People with Type 1 diabetes must replace insulin from outside the body, typically through injections or a pump, for the rest of their lives. There is no way to restart the destroyed beta cells.
Type 2: From Resistance to Deficiency
Type 2 diabetes follows a different path. Early on, the pancreas actually produces plenty of insulin, sometimes more than normal. The problem is that cells throughout the body stop responding to it properly, a condition called insulin resistance. The pancreas compensates by cranking out extra insulin, but over time that overwork damages the beta cells themselves.
In long-standing Type 2 diabetes, beta cell mass declines by 20 to 40%. The insulin secretion deficit gets progressively worse as blood sugar stays elevated, a vicious cycle driven by the toxic effects of chronic high glucose and high fat levels on the remaining beta cells. So while Type 2 diabetes starts as a problem of insulin resistance, it eventually becomes a problem of insulin deficiency too.
Amylin: The Overlooked Missing Hormone
Beta cells don’t just make insulin. They also produce a lesser-known hormone called amylin, which is released alongside insulin every time you eat. When beta cells are destroyed or worn out, amylin production drops right along with insulin.
Amylin plays several roles that matter for blood sugar control. It slows down how fast food leaves your stomach, which prevents a sudden spike of sugar hitting the bloodstream all at once. It also dials back the release of another pancreatic hormone called glucagon, which would otherwise tell the liver to dump more sugar into the blood. And it sends signals to the brain that help you feel full after eating.
Losing amylin means food empties from the stomach too quickly, glucagon goes unchecked, and post-meal blood sugar spikes become harder to control. Standard insulin injections replace insulin but not amylin, which is one reason why managing blood sugar after meals remains a challenge even for patients on insulin therapy.
Glucagon Excess: Too Much of the Wrong Hormone
Diabetes isn’t just about what’s missing. It’s also about what’s present in excess. Glucagon, produced by alpha cells in the pancreas, normally raises blood sugar when levels drop too low, such as between meals or during exercise. In a healthy pancreas, insulin from neighboring beta cells keeps glucagon in check through a direct feedback loop.
When insulin disappears, that feedback loop breaks. Alpha cells keep pumping out glucagon even when blood sugar is already dangerously high. In one study, people with Type 1 diabetes who had their insulin withdrawn for 14 hours continued secreting glucagon despite blood sugar levels around 360 mg/dL, nearly triple the normal fasting level. When insulin was reintroduced intravenously, glucagon levels quickly dropped.
This combination of too little insulin and too much glucagon is sometimes called the “bihormonal hypothesis” of diabetes. It means the liver keeps producing and releasing sugar into the blood even when it shouldn’t, making hyperglycemia worse than insulin deficiency alone would explain.
Incretin Hormones and Gut Signaling
Your gut produces its own set of hormones that help manage blood sugar after you eat. The two most important are GLP-1 and GIP, collectively called incretins. When food reaches your intestines, these hormones signal the pancreas to ramp up insulin production in advance of the incoming sugar.
In Type 2 diabetes, this system breaks down in two ways. GLP-1 levels after meals tend to be lower than normal, partly because the enzyme that breaks it down is overactive. Meanwhile, GIP is actually released in normal or even elevated amounts, but the pancreas becomes resistant to its signal, so it fails to trigger adequate insulin release. The net result is that one of the body’s early-warning systems for managing post-meal blood sugar stops working effectively.
This is why a major class of diabetes medications works by mimicking or boosting GLP-1 activity. These drugs compensate for the weakened incretin response that develops alongside insulin problems.
What Happens When Insulin Disappears Completely
The most dangerous consequence of total insulin absence is a chain reaction that produces acidic chemicals called ketones. Here’s how it works: without insulin, fat cells release large amounts of fatty acids into the bloodstream. The liver takes up those fatty acids and begins breaking them down for energy. This process generates a molecule called acetyl-CoA faster than the liver can burn it through normal pathways. The excess gets converted into ketone bodies, primarily two types that can serve as emergency fuel for the brain, heart, and muscles.
In small amounts, ketones are a normal backup energy source. But without insulin to slow the process, ketone production spirals out of control. The blood becomes increasingly acidic, a life-threatening condition called diabetic ketoacidosis. This is most common in Type 1 diabetes and is sometimes the very first sign that leads to diagnosis.
How Insulin Deficiency Is Measured
Diabetes is diagnosed through blood sugar levels, not by measuring insulin directly. The American Diabetes Association recognizes several thresholds: a fasting blood sugar of 126 mg/dL or higher, a blood sugar of 200 mg/dL or higher two hours after drinking a standardized glucose solution, or an A1C of 6.5% or above (A1C reflects average blood sugar over roughly three months). Any one of these, confirmed by repeat testing, establishes a diagnosis.
To determine how much insulin the body is still making, doctors use the C-peptide test. C-peptide is a byproduct released in equal amounts whenever the pancreas produces insulin, so its level in the blood mirrors actual insulin production. A C-peptide below 0.2 nmol/L points to severe beta cell loss and near-absolute insulin deficiency, which typically means the patient needs insulin therapy. Higher C-peptide levels suggest the pancreas still has some working capacity, which is more common in Type 2 diabetes and may allow for treatment with non-insulin medications.