What you need to know about carbs, part 3: Can you go too low carb?

Silvia Hua
Defy Time Fitness
Published in
3 min readApr 7, 2020


Photo by Kelly Sikkema on Unsplash

Do we even need carbs?

Technically, the calories you get from vegetables and fruits are mostly from carbohydrates. Something like spinach can be low carb but still mostly carb. Vegetables and fruit are a great way to get lots of micronutrients (vitamins, minerals, antioxidants, and other beneficial stuff) as well as fibre, so should generally be included in everyone’s diet.

A common misconception people have is that complex carbs are healthy, and I think that’s partly because they assume complex carbs means fibre (not technically true). While healthier sources of carbs will tend to have complex carbs, many less nutritious foods like white bread, Cheetos, and tapioca pearls are technically mostly complex carbohydrates (starch) as well. What’s more important — and likely what most people think of when it comes to selecting better carbohydrates — is to look at the source:

  • How much micronutrients and fibre does it have?
  • How processed is it?
  • Will this make me feel good after, or will it make me feel tired/bloated/anxious/overeat or give me joint pain/acne/brain fog?

Precision Nutrition’s healthy eating guidelines uses the term “smart carbs”, which can include fruit, starchy vegetables, tubers, whole grains, and other minimally processed carbohydrate sources. I love this term because:

  • It automatically rules out most high sugar foods and selects for higher fibre options.
  • It does NOT mean you need to include grains in your diet! You can get plenty of carbohydrates from other whole food sources.

What happens if we avoid carbs?

Of all the macronutrients that we eat, the body can make energy the most rapidly from carbohydrates. Not having enough carbohydrates in the body can impair your athletic performance and your ability to get good workouts. Beyond that, going low carb for a long time can have other undesirable effects.

Short term:

  • It can impair your body’s ability to make melatonin, which is important for falling asleep and staying asleep.
  • If your body’s blood sugar gets too low while you’re sleeping, you may wake up prematurely due a rise in stress-related hormones (including cortisol).

Long term:

  • The disrupted sleep has a host of other negative effects, including mood issues, lethargy, poor blood sugar regulation, cognitive impairment, and increased cravings.
  • Cortisol levels become disrupted. Cortisol is an important hormone for survival and for feeling energized, but when it is chronically higher than it should be (such as what happens when under any physical or mental stress), it has a lot of negative effects on your health and makes it harder to gain muscle and easier to store belly fat.
  • The chronic state of stress from being too low carb (even if you don’t perceive it) can decrease sex hormones (e.g. estrogen, testosterone), which has many other serious downsides. Women are more likely to experience this. Other factors that increase risk for disrupted sex hormones from not having enough carbs include high stress levels, high exercise intensity/duration, low body fat, and lower nutrient intake.

How will I know if I am going too low carb?

Here are some possible signs that you are not eating enough carbs for your current situation:

  • Feeling cold.
  • Feeling more tired than usual.
  • Hair loss.
  • Body aches, pain, or injuries (both minor and serious).
  • Less frequent or absent menstruation in women (definitely a serious sign!).
  • Difficulty falling or staying asleep.
  • Poor mood (anxiety, depression, low self-esteem).
  • Higher cravings for sweets or starches.
  • Disproportionately high body fat in the midsection.
  • Lower heart rate and blood pressure than expected.
  • Digestive problems (usually bloating and/or constipation).
  • Feeling dizzy more easily (orthostatic hypotension).

Of course, the symptoms above can have many different causes other than not eating enough carbs. This article is not a comprehensive medical guide, so do talk to a qualified doctor or dietician for personalized care if you are experiencing health problems.

That’s it for my 3-part series on what you need to know about carbs. Have more questions? Get in touch!



Silvia Hua
Defy Time Fitness

Exercise physiologist and data scientist. @silvialiftsweights