To Fast, or Not to Fast?

by karen on April 26, 2018

I have to admit, as a dietitian educated several decades ago, I cannot recall being taught that we should go out into the world and educate our clients on the merits of fasting.  I left college with the firm belief that the ‘best’ way for all of us to eat was to eat regularly throughout the day.

So, when four clients in the span of mere days asked my opinion on fasting for weight loss, I knew I had to do some research.  That’s what I do when I don’t have the answers, what I was trained to do: look at the research.  Dietitians are nothing if not health professionals that strive to have our clients avoid fads and the latest in diet crazes, but this day and age we are all virtually bombarded with the ‘best’ and ‘only’ way to achieve a healthy weight and be the healthiest version of ourselves.

Here’s what I see when searching for the facts on the ‘best’ diet:

There is no one right diet for everyone

If you know me, you’ve no doubt heard me say countless times that I hope I’m still in the game of nutrition when nutrigenetics becomes a valid way to determine one’s ideal diet.  In theory, you would bring in your DNA test results and we could see how foods affect you, both positively and negatively, and from there, build a very clear plan of your ‘ideal diet’.  We are getting closer to being able to look at our DNA to know what each of our bodies needs to thrive on, and that may be vastly different from one individual to the next.  But we’re not there yet.  Until then, science shows us there are factors that must be considered when figuring out the ‘best’ diet.

5 legitimate components that affect weight and health

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  1. Genes.  While waiting for DNA diet recommendations to become reality, we have personal medical history, family medical history, food allergies and intolerance, and body weight, body composition and weight history that have a genetic basis.  This is why you are asked for all of this information when being seen for nutrition consultation.  A detailed medical history gives us a glimpse into how your body functions on a cellular level, and we go from there.

See the source image

  1. Environment.  We’re born with our genetic makeup and that has a very large influence on our health as we go through life, but environment is there every step of the way.  How were you raised to eat?  Did you learn to cook or did you grow up on fast food?  Were you introduced to vegetables before the age of 5 so you’d have an opportunity to like them?  Skip to present day – do you eat a donut whenever they’re in the office, simply because they’re there and without regard to your hunger level or when you last ate?  Do you snack on chips at night because your significant other is eating them while sitting next to you?  Our environment, past and present, has a big influence on our weight and health.

  2. Metabolism.  For the rare individual‒you know who you are‒who can eat and drink whatever, whenever and never gain weight: you won the “high metabolism gene”.  From day one, your body burns more calories moving you through the day than your everyday Joe compadres.  Be grateful, but be careful.  Just because you maintain a weight the rest of us envy and have to be conscientious not to hold against you, you have not necessarily been given the health gene (whatever that is).  Being thin does not equate to being healthy.  Thin people still get diabetes and heart disease, just like the overweight majority of us.  If you were born with a slow metabolism, which is a legit condition, you will not be successful with weight or health using it as an excuse.  You have to work harder and be more diligent with your food intake.  Accept it.  You’re in a big boat with a majority of your cohorts.  Find the support to find a lifestyle that is healthy for you.

  3. Hormones.  This is a tricky one that is challenging to get proper insight on to incorporate into a healthy eating plan.  There are companies that claim to do this, but the science isn’t there to support their recommendations.  Half-truths are often used to sell the concept and a lot of money can be chased down the rabbit hole following these types of plans.  You know hormones rule the roost when kids go through puberty; their bodies change largely as a result of hormonal changes, the same when women are pregnant; the pelvis widens and breasts enlarge (totally hormonal).  If you’re a female of a certain age, you can attest to the myriad of changes the body goes through after menopause.  But to take hormones, like with the HCG diet, is a risky proposition and one where I’ve never seen lasting results.  Don’t waste your time Googling ‘hormone diet’ – you’ll find dozens of options, all poised to set you up for another failure.  But with that said, we can take hormones into account when helping determine your best diet.

  1. Behavior.  After the rest is reviewed, this is where I like to focus time and energy to help my clients achieve their goals and find their ‘best’ diet.  How we behave on a daily basis has a huge affect on who we are, including how healthy we are.  Our food beliefs started when we started, we learned from modeling our family.  We don’t even think about and are often unaware of our food beliefs, rarely questioning their basis or whether they are founded in truth.  Our habits are challenging and time-consuming to change, but can net lasting results when our healthy plan is maintained a majority of time, say 75%.  That’s to say that if you can eat well 3 out of 4 meals or make 3 of every 4 food choices from your plan or avoid trigger foods 3 out of 4 times, you will be successful.

Back to fasting as a successful means of losing weight/being healthy.

One of the most important points to consider before starting on a fasting or any eating plan is to acknowledge that the results you achieve will only be maintained by maintaining the behaviors that got the results in the first place.  If you can follow a plan that involves fasting, whether it be alternate day fasting, 16 hour fasting, 5:2 fasting, or any other plan currently out there, on an ongoing basis for the rest of your life, you might benefit from a fasting plan. But if you do not believe you want to live this way forever, there may be no long-term benefit to a fasting diet.  There are also no studies available showing long-term results.

You might consider fasting in the short-term, as there is short-term evidence that various fasting plans can reduce the risk for diabetes and heart disease, promote fast weight loss, lower insulin levels, and help manage diabetes.  Despite the concern that the brain will be deprived of necessary glucose needed for fuel, studies show that once the body is deprived of food carbohydrate in the form of grain, dairy, fruit and of course, white flour and sugar, the body will deplete its stores of glucose.  After that, the body taps into stored fat cells for energy, at which time, the brain as well as the body runs on a compound known as ketone bodies.  And studies show ketone bodies can provide energy for day-to-day activities and exercise without fatigue.  There is also little hunger when our diet and bodies are devoid of glucose.  I must admit I had forgotten or hadn’t learned in my initial education that ketone bodies can be a healthy form of energy.

A fasting meal plan might be of benefit to:

  • Break a cycle of poor eating habits that have become so entrenched you cannot start/follow a new plan for even a day

  • Get away from the mental and physical dependence of eating on a schedule and instead, eat intuitively

  • Give you confidence that you can make changes in eating and that you won’t die if you skip a meal or two

  • Jump-start weight loss

Fasting should be avoided in the presence of:

  • Type 1 diabetes

  • Type 2 diabetes on medications unless under medical supervision

  • If you experience low blood sugar (hypoglycemia)

  • An eating disorder

  • A tendency to binge eat

  • A habit of restricting food that has not resulted in improved health

  • Low body weight

Side effects to be aware of:

  • Constipation

  • Dehydration observed with loss of energy, dry skin, extreme thirst

  • Electrolyte imbalances that can affect normal heart rhythm

  • Micronutrient deficiencies – low levels of vitamins and minerals

  • Low blood sugar – sudden onset of shakiness, irritability, cold sweats, extreme fatigue, with the need for glucose to overcome

If you experience any of these symptoms, it is a sign your body is not doing well with a fasting/starvation diet.  Following intuitive eating, where you listen to your body, you would likely stop the fast.

While various forms of fasting are popular in the current world of health and weight management trends, science shows time and again you will go much further incorporating a balanced, unprocessed diet rich in colorful fruits and vegetables, whole grains, nuts, seeds, fish and olive oil, with lean meat and dairy if you choose to incorporate animal foods, eaten often enough throughout the day to be hungry but not over hungry at your next meal or snack.  A good goal to strive for in achieving a healthy lifestyle with a healthy weight.

Karen Fisher, MS, RDN, CDE is a dietitian in Reno, Nevada, happily promoting the benefits of healthy foods at her nutrition consulting firm, Nutrition Connection. Find her website at

{ 2 comments… read them below or add one }

Loran May 2, 2018 at 2:44 am

You’re on top of the game. Thanks for shanrig.


Betsy Clark May 2, 2018 at 8:21 am

Good info, Karen. Thank you!


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