The concept of clean eating involves eating minimally processed foods as close to their natural state, such as fruits, vegetables, whole grains, and legumes. However, there can be major downsides to clean eating practices when they are too restrictive, such as cutting out carbohydrates.
To better understand the nutrient gap in clean eating, we spoke with Lissa Denis, RDN, LD/N, CEDS-C, director of nutrition at Monte Nido, an institution that specializes in the treatment of eating disorders.
Q: How does it make a person feel when they cut out or decrease their intake of carbohydrates in the name of clean eating?
Denis: Carbohydrates are the body’s preferred energy source, and when dietary carbs are insufficient, the body uses its stored form, glycogen, causing an initial loss of water weight.
Carbohydrates also provide energy, fiber, essential micronutrients, and are a major component of many enjoyable and satisfying foods. Restricting them can increase irritability, low mood, food preoccupation, and risk of binge eating.
If you cut out carbohydrates, you may experience a group of symptoms known as “keto flu” that can leave you feeling really lousy. With prolonged restriction, fat is broken down into ketones for fuel. These metabolic shifts can lead to fatigue, headaches, dizziness, brain fog, bad breath, decreased exercise performance, constipation, and altered hormone levels.While the body can adapt to using ketones as fuel in the absence of glucose, the transition takes time, during which energy levels are low.
Carb restriction can also affect hormones, digestion, electrolyte balance, and the brain’s neurotransmitters, all of which can contribute to feeling unwell physically and mentally.
Q: Can clean eating affect your thyroid hormones? Can that make you feel even worse?
Cutting out carbohydrates can also disrupt your thyroid hormones, and this can lead to a sort of chain reaction in your body. Thyroid hormones regulate metabolism, body temperature, heart rate, and growth. Carbohydrate restriction can reduce your thyroid’s ability to convert T4 into the more active T3.
When carbohydrate intake is very low, the body may downregulate metabolism to conserve energy. This slows the activity of enzymes that convert T4 to T3, leading to lower circulating active thyroid hormone and higher inactive reverse T3 (rT3).
This can make you feel brain fog, sluggish, and cold, even if thyroid hormone production itself is normal.
Q: Why is ‘clean eating’ advice harmful for your mental health?
Denis: “Clean eating” frames food in moral terms instead of focusing on overall patterns and individual physiology. Nutrition is complex and only one component of health. Labeling foods as “clean” implies others are “dirty,” which fuels guilt, rigidity, and all-or-nothing thinking.
This mindset often shrinks food variety, increases anxiety around social eating, and can quietly mask disordered eating patterns under a socially acceptable label. It also ignores cultural foods, economic circumstances, and the reality that processing often improves food safety and nutrient availability.
Consider shifting your focus to your relationship with food—one built on trust, adequacy, variety, and permission rather than guilt, fear, or extreme thinking.
It can be helpful to reflect on the food values that guide how and why you eat. These might include nourishment, satisfaction, connection, culture, access, or performance. When your food choices reflect a range of values, eating becomes more flexible, attuned, and sustainable, supporting both your physical health and overall well-being.
If you need help doing this, a dietitian or nutritionist can help. “If you’re having concerns about your own or a loved one’s relationship with food and nutrition, help is available,” Denis said.
If you or a loved one is living with an eating disorder, contact the National Alliance for Eating Disorders Helpline at 1-866-662-1235 for support and referrals.
