Dr. Harris on Intermittent Fasting

Dr. Harris on Intermittent Fasting

What is Intermittent Fasting?

Intermittent fasting is a popular eating pattern that cycles between periods of eating and fasting. It is also known as time-restricted eating. While technically these terms refer to different strategies the main-stream conversation describes it as a diet based around when to eat versus what to eat. 

Typical fasting / eating patterns are:

  • The most common: 16 / 8: Eat all of your meals within 8 hours and fast for 16
  • More extreme variants include adding time to the fasting window while subtracting time from the eating window (i.e. 20 hours of fasting and 4 hours of eating)

Intermittent fasting has been shown to help regulate blood sugar levels, increase human growth hormone, induce cellular repair, increase expression of longevity genes, decrease body fat, reduce stress and inflammation, and improve cognition.

Check out Dr. Harris’s podcast and blog here for more information on the benefits and pitfalls to intermittent fasting and how to incorporate it into your life.

Common Nutrient Deficiencies to Look Out For:

If you’re eating a low(er) carbohydrate diet, intermittent fasting can push the body into ketosis and you kind experience similar nutrient deficiencies as you would in a keto diet. This tends to only occur over time on a low to very-low carbohydrate diet and exercise can further push the body towards ketosis in these instances.

  • At the start, you may can see lower levels of electrolytes with decreased sodium and potassium due to lower insulin levels. Dehydration can also become a concern as insulin levels drop and your body retains less water.
  • Calcium, which also functions as an electrolyte, is another common nutrient deficiency due to increased urinary excretion of ketones.

A key driver in the efficacy of intermittent fasting / time restricted eating is that this method of food consumption typically results in a caloric deficit. Since you are eating larger meals (as you typically miss a meal and have less time to eat), you feel fuller during the eating window and often eat fewer calories. Food restriction, especially in the presence of nutrient poor diet, can exacerbate nutrient deficiencies.

Dr. Harris also has a podcast and blog post related to nutrient deficiencies that you can find here.

How to Solve These Potential Deficiencies:

The first step is to determine if this is a strategy that will work well for your body. While there is much nuance in this topic and every case should be assessed by a professional individually (if you plan to do this for a longer period of time) if you commonly struggle with nutrient absorption issues or your gastrointestinal system is sensitive to larger volumes of food, this may not be a good strategy for you.

The key to maintaining health while fasting is to make sure that you are eating nutrient dense foods and ensuring your caloric deficit, if present, is not too large. Eating nutrient dense foods will keep your daily nutrient intake adequate, although additional support may be needed depending on the circumstances, and an overly large caloric deficit (read: greater than 15%, although this varies from person to person) is not a key to long-term success.

How do you do this?

  • Eat the rainbow and ensure you are eating a wide range of fruits, vegetables, and other whole foods. In general, diets with a larger swathe of foods tend to have better nutrient profiles.
  • Test to better understand your bodies specific needs, and ensure those needs are being met over time.
  • Supplement with vitamins and nutrients as needed.

What Tests Should I Focus On?

DNA Testing:  A vitamin DNA test can tell you which nutrients you may inherently need more or less of, giving you a baseline to better understand how to hit your goals

Blood Testing: Testing key biomarkers found in the blood can help you understand where your current levels are and if they are within normal range. 

  • Biomarkers that can be important for individuals that are intermittent fasting include Vitamin D levels, homocysteine levels, b vitamin levels, CBC, CMP, and hsCRP.
  • Testing for iron and folate will also provide an idea if you need to incorporate more protein or vegetables into your diet.


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