If the popularity of the keto diet has proven anything, it’s that fat is not the enemy. According to the American Heart Foundation, healthy dietary fats give your body the energy it needs, help lower levels of ‘bad’ cholesterol, provide the building blocks for hormones, and help your body absorb fat-soluble vitamins (A, D, E, and K).
If you don’t get enough of it, your body might not be able to do some very basic but important tasks, including protecting you from free radicals (which are linked to chronic disease), supporting healthy skin and nails, and keeping you warm, says Abby Vichill, R.D., a registered dietitian with holistic food blog FWDfuel Sports Nutrition.
Another reason to fuel up on fat: Your body can’t create certain fats called essential fatty acids, which it needs to operate at full strength, on its own. Instead, you have to get them from foods like flax seeds, walnuts, and salmon.
A simple rule of thumb: Try to include a serving of heart-healthy unsaturated fats (chia seeds, olive oil, avocado, mixed nuts, or fatty fish) with each meal. At a bare minimum, dietary fats should make up 20 percent of men’s total daily caloric intake and 25 percent of women’s, according to the Mayo Clinic.
What Happens When You Fall Short On Dietary Fat
If you clock in below the recommended dietary fat levels, you might notice the following symptoms.
1. Your Hunger Could Go Through The Roof
High-fat foods help you produce the hormone leptin (a.k.a. the satiety hormone), which tells your body when you have enough energy and can put your fork down, says Vichill. Without enough fat—and enough of this appetite-suppressing hormone to tell you you’re full—you could wind up super-hungry and overeat, which could lead to weight gain.
2. Your Skin Could Suffer
Research, such as this 2011 Journal of Oleo Science study, suggests that omega-3 fatty acids found in mackerel, salmon, walnuts, and flaxseeds may help support healthy skin cells. These fats effectively improve your natural skin barrier’s ability to seal in moisture and keep your skin hydrated and smooth.
Read More: How To Eat For Healthy Skin
3. Vitamins May Not Be Able To Do Their Jobs
Dietary fat must be present in order for your body to absorb vitamins A, D, E, and K. Without enough fat in your diet, you may have trouble absorbing and putting these important nutrients to use.
True deficiencies in vitamin A, K, and E are rare. However, insufficient levels might affect your vision and make you more prone to illness and bleeding issues, says Vichill. If you’re low on vitamin D—a much more common occurrence—you might struggle with brain fog and a dip in mood and energy. (Recent research out of the British Journal of Psychiatry also suggests there may be a link between vitamin D deficiency and depression.)
4. Your Mental Health Could Suffer
People on a diet rich in polyunsaturated and saturated fats feel better and less irritable than they do on a low-fat diet, per a 2016 study in Biological Research for Nursing.
This may be, in part, because your brain and nervous system rely heavily on fats to function, says Vichill. Omega-3 fatty acids (which are polyunsaturated fats), in particular, support neurotransmitters and metabolic processes that keep your brain in shape. In fact, one JAMA review links omega-3s with improved mental health.
5. Your Endurance Might Get Zapped
According to the National Institutes of Health, your body begins to rely more on fats for fuel after 20 minutes of exercise. (No wonder some elite endurance athletes love keto!)
That said, if you want to run, bike, or hike farther, fat is actually your friend. In fact, after more than an hour of movement, fat becomes your primary fuel source, so if you’re low, you might hit a wall.
6. You Could Throw Your Reproductive System Out Of Whack
Women who go super-low on fat may begin to have irregular periods and struggle with fertility, says Vichill. (Trouble can start to crop up when intake drops below 15 percent of caloric intake or 50 grams a day.)
Hormones are actually made from fat and cholesterol, so if you don’t have enough of these building blocks, your body produces less of them. Fat is especially crucial for luteinizing and follicle-stimulating hormone production, which women need to ovulate, Vichill says.
For men, too little dietary fat can contribute to a decrease in testosterone production—and dips in libido and athletic performance.
References & Further Reading On Dietary Fat
- Journal of Oleo Science: Dietary supplementation of gamma-linolenic acid improves skin parameters in subjects with dry skin and mild atopic dermatitis.
- American Heart Foundation: Dietary Fats
- British Journal of Psychiatry: Vitamin D deficiency and depression in adults: systematic review and meta-analysis.
- Biological Research for Nursing: Neurobehavioral Effects of Consuming Dietary Fatty Acids.
- JAMA: Direct and Indirect Effects of Leptin on Adipocyte Metabolism
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