There are a host of diet plans available claiming to promote rapid weight loss. A low-carb diet is a popular diet plan in which only 15 to 20 percent of your calories come from carbs and the rest come from fats and proteins. (ref 1, sec 2) You may be drawn to this diet if you like protein-rich foods, but like any other diet, a low-carb one has its pitfalls. Carbs, found in grains, fruits, vegetables and dairy products, are a key energy source for your brain and body. Without sufficient carbs, your brain won't be able to produce enough feel-good hormones and you may suffer from nutritional deficiencies that are linked to depression. Keep tabs on the foods you eat and how they affect your mood and consult with your physician or registered dietitian before embarking on a low-carb diet.
Depression, Carbs and Serotonin
Clinical depression involves feelings of sadness and despair that last for several weeks and interfere with your daily living. It also causes difficulty sleeping, lack of energy, changes in appetite, trouble concentrating, feelings of guilt and hopelessness, avoiding activities you previously enjoyed and suicidal thoughts. Depression is influenced by your genes and can be brought on by stress. (ref 3, sec 1 and 2 bullet points)
Hormones and neurotransmitters – chemicals that transport nerve signals in your body - influence depression. The neurotransmitter serotonin improves your mood, enhances sleepiness and relaxation and promotes feelings of satisfaction after eating. (ref 2, para 1)
Carbohydrates increase your serotonin levels. After eating a meal rich in carbs, your body releases the hormone insulin. Insulin enables the amino acid tryptophan to enter your brain and produce more of the feel-good hormone serotonin (ref 2, para 3) By restricting carbs, your brain might not be able to manufacture enough serotonin and your mood will suffer.
What Does the Research Say?
Research is mixed on whether or not a low carb diet contributes to depression. A study published in 2009 in the "Archives of Internal Medicine" assigned overweight or obese adults to either a low-carb, high-fat diet or a low-fat, high-carb diet for one year. Both groups consumed the same amount of calories. Subjects were tested for weight, mood and brain function throughout the year-long study. While both groups lost weight, the low-carb dieters showed significantly higher scores on anger, confusion and depression. The researchers attributed the results to dieters feeling deprived because they are constantly surrounded by bread and pasta in the typical Western diet and low serotonin levels in the brain. (ref 5, abstract, results and conclusion and resource 1)
By contrast, a study published in 2007 in the "The American Journal of Clinical Nutrition" assigned obese adults to a low-carb, high fat diet or a high-carb, low-fat diet. The results indicated both groups lost weight, but the low-carb dieters lost more weight and both groups showed enhanced mood. (ref 6, abstract) Another study published in 2007 in “Appetite” assigned obese women with polycystic ovary syndrome to the same two groups as the aforementioned study. The results showed women in the high-protein, low carb group had reduced feelings of depression and enhancement in their mood. (ref 7, abstract)
Depression: More Than Serotonin
While a diet low in carbs may deplete your serotonin levels, there is probably more to your depressive symptoms than a lack of carbs. Selective serotonin reuptake inhibitors -- a class of drugs that boost the level of serotonin activity in your brain -- are widely prescribed anti-depressant medications. But an article published in 2013 in “Philosophical Transactions of Royal Society B” stated they are only effective in 50 percent of patients. (ref 4, sec 4) indicating there is more to depression than low serotonin levels. That means that, while it's possible diet might contribute to depression in some cases, that's not the case for everyone.
Nutritional Deficiencies on a Low-Carb Diet
Your low-carb diet is probably not directly causing your depression, but depriving yourself of carbs deprives you of important nutrients that may lead to depressive symptoms. If you are a vegan following a low-carb diet you may not be getting adequate vitamin B-12 (ref 8, sec 2, para 2). Eventually, low B-12 levels can damage your nerves, leading to memory loss, confusion and depression according to “Harvard Health Publications.” (ref 8, sec 1, para 1) While vegetarians can get B-12 through eggs and dairy -- and it's also available in meat and fish -- vegans should eat fortified foods
Fiber is a key nutrient in whole-grain products, fruits and vegetables. Adequate fiber intake can reduce your feelings of depression as you age, according to a study published in 2016 in “The Journal of Gerontology.” They discovered that adults who consumed more dietary fiber from cereals, breads and fruits had lower rates of cognitive problems and symptoms of depression. (ref 9, abstract)
Instead of restricting your carbohydrate intake, consider reducing your portion sizes and opting for carbohydrates high in fiber. Most likely, your glum feelings aren’t coming from the foods you eat, especially if your low-carb diet is short-term. You also need to consider how much sleep you’re getting, medications you’re on, your exercise routine and your stress levels. (ref 2, sec 5)