Sugar Could be Making You Depressed

For decades, psychiatrists have believed that depression is caused by a deficiency of chemical messengers known as neurotransmitters. A lack of these chemicals has been touted as the cause of depression, and antidepressant medicines were believed to work by increasing them. But about one third of patients with depression don’t respond to conventional antidepressants. This suggests there’s more to this story, and new research suggests that our blood sugar may be a missing piece in the depression puzzle.

Why Your Brain Cares About Blood Sugar

Our brain makes up about 2% of our body weight, but it uses about 20% of our body’s energy. Most of that energy comes from glucose, which is the sugar found in our blood. Our bodies use insulin to move glucose from the blood into our cells. You can think of insulin as a key that unlocks cells so sugar can get in.

But when this system gets overloaded, it causes problems. When we eat food that contains a lot of carbohydrates (e.g. sugars and starches), our blood sugar can shoot up quickly and then crash. Over time, our body needs more and more insulin to get the same results. Eventually our cells can become unresponsive to insulin. This is called insulin resistance, and it can lead to type 2 diabetes.

The Link Between Insulin Resistance and Depression

It has been known for a long time that people with diabetes are twice as likely to be depressed as people without it. But which comes first – diabetes or depression?

A study of 601 adults who were not depressed was conducted over nine years. The study found that people with signs of insulin resistance were much more likely to develop depression. A rise in the ratio of triglycerides to HDL cholesterol was associated with an 89% higher rate of new depression, and a rise in fasting blood sugar was associated with a 37% higher rate. This showed that problems with blood sugar control developed before depression did.

Diet matters too. In another study involving nearly 70,000 women, those who ate diets with a high glycemic index (i.e. foods that spike blood sugar quickly) were more likely to develop depression. Women who ate more fiber, whole grains, vegetables, and fruit were less likely to become depressed.

What about the “sugar rush”? A review of 31 studies found that sugar doesn’t lift mood. Within an hour of eating it, people actually felt more tired and less alert. The sugar rush is mostly a myth. But the sugar crash is real.

Where Ultraprocessed Foods Come In

Ultraprocessed foods are products made from refined ingredients and additives. Examples include sodas, packaged snacks, sweetened cereals, fast food, and many frozen meals. These foods are often loaded with sugar and starch, which cause our blood sugar to swing high, then low.

A review involving data from nearly 10 million people found that eating more ultraprocessed food was linked to a 22% higher risk of depression and higher risks of anxiety, type 2 diabetes, and heart disease. Another study of more than 31,000 women found those who ate the most ultraprocessed food had a 50% higher risk of depression than those who ate the least ultraprocessed food.

Studies like these show there’s a connection between eating ultraprocessed food and depression, but they don’t prove that eating these foods causes depression.

Metabolic Psychiatry: Dr. Shebani Sethi’s Work at Stanford

A doctor who has done amazing work in this area is Dr. Shebani Sethi. A psychiatrist and obesity medicine specialist at Stanford, Dr. Sethi coined the term “metabolic psychiatry” to describe a new field that studies and treats the connection between metabolic problems and mental illness.

Dr. Sethi’s focus is simple. She points out that the brain uses a lot of energy, and when the body’s energy system breaks down, the brain suffers. In a review, she and her colleagues described how depression, bipolar disorder, schizophrenia, and binge eating disorder all share similar problems, including poor utilization of glucose by the brain, imbalanced brain chemicals, oxidative stress, and inflammation. In another review, Dr. Sethi and Dr. Judith Ford noted that insulin resistance is a risk factor for depression.

Dr. Sethi has also written about how ultraprocessed and refined carbohydrates can trigger blood sugar and insulin spikes that cause cravings and overeating in a way that resembles drug addiction. This helps explain why it can be so hard to eat less of these foods.

Her best-known study tested a ketogenic diet (which is very low in carbohydrates) in 21 adults with bipolar disorder or schizophrenia who also had metabolic problems. These patients stayed on their medications. After four months, the number of people who met the criteria for metabolic syndrome dropped from 29% to zero. Their weight, waist size, blood sugar, and insulin resistance all improved. Also, their psychiatric symptom severity dropped by 31%.

In 2026, Dr. Sethi and her colleagues published their recommendations on using ketogenic therapy in adults with major depressive disorder, bipolar disorder, and schizophrenia. Her team at Stanford is also running a larger randomized trial that includes people with major depression.

What This Research Tells Us

It would be a mistake to say that blood sugar causes all depression. It doesn’t. Depression has many causes. Most of the studies linking diet and depression don’t prove high sugar causes depression.

But the evidence is growing that insulin resistance often develops before depression, and diets that spike blood sugar are linked to a higher risk of developing depression. Also, when people with depression and metabolic problems change how they eat, their mood often improves.

The Bottom Line

Our brain doesn’t exist in a vacuum. It depends on the rest of our body for fuel, and when that fuel supply is unstable, we may experience mood changes. New research, including the pioneering work of Dr. Shebani Sethi suggests that one of the most powerful tools for improving our mood may be changing what we eat.

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