The potential health benefits associated with intermittent fasting continue to be a topic of great interest to myself, my clients and the public at large.
I’ve admitted in a previous blog post that, although I don’t regularly adhere to fasting principles, I do engage in fasting on occasion if I feel like my hunger levels are lower than I’d like them to be.
I use it infrequently and primarily as a tool to build up my hunger for a larger meal later in the day, not for any supposed or potential health benefits it may offer.
I certainly recommend you check that one out as well, but the reason I am back talking fasting again today is that I received a suggestion from a reader that perhaps there were some facets to fasting that I missed.
And so here I am re-visiting the topic!
Intermittent fasting is a VERY popular subject area and so I really have no issue kicking off round two exploring the literature for high quality human evidence on the metabolic benefits of fasting.
Let’s take a look at what I came up with this time.
Why Do You Want To Fast?
Before we go any further I think it’ very important to address the why.
Many of my clients express interest in learning more about fasting and potentially trying it for themselves.
To this query I must always ask why?
If fasting represents a gimmick or means to achieve some short-term goal,that right there is a sign that it is not a good choice for you.
If, however, intermittent fasting is an area of interest that fits within the context of your lifestyle, is enjoyable to you and supports you eating a high quality nutrient dense diet, then you find yourself in a situation where it could be worth a try.
Intermittent fasting, like anything else, comes stocked with a list of theoretical benefits that may be partially supported by some level of literature evidence in either animals or humans.
1) Improved Fat Loss: In theory, because your body prefers to “burn fat” for fuel in a fasted state, it has been suggested that intermittent fasting may be superior to standard calorie reduction in supporting reductions in body fat.
I’ve not found any high quality human studies which suggest this to be the case but when it comes to general weight loss using intermittent fasting there are some things to keep in mind:
A systematic review and meta-analysis of human intervention studies using intermittent fasting as a weight loss treatment found it no more effective than continuous energy restriction.
There is also little evidence that intermittent fasting is superior at modulating resting energy expenditure(REE). REE, in essence, is the amount of energy a body expends at rest and not including other activities that would also require energy.
Some have suggested that fasting “boosts” your metabolism and one potential way to assess that is by measuring changes in resting energy expenditure in people doing intermittent fasting vs more conventional caloric reduction strategies.
No high quality evidence so far to show a compellingly differential effect.
2) Metabolic Flexibility: Because your body flips to fat metabolism in a fasted state, alterations occur on the cellular level ( including to your mitochondria) which some scientists suggest can promote what is known as metabolic flexibility, ultimately improving the health of your metabolism and functioning of your body on a metabolic level. Some believe, for example, that lacking metabolic flexibility contributes to insulin resistance in the long-term. Much more human evidence on the effects of fasting on this phenomenon will be required before firm conclusions can be drawn in this area.
3) Cellular & Metabolic Revitalization: This one is interesting and quite hard to prove with the current state of evidence, but some scientist suggest that the stress induced by fasting actually helps your bodily systems in the long-term. You can think about this along the same lines of taking a cold shower or an ice bath. It may not be particularly pleasant in the moment, but there are benefits to be had after it’s over.
Obviously further exploration and evidence will be required in this area but, to say the very least, the first meal one enjoys post-fast is highly enjoyable and reward on a number of levels ( speaking from limited experience!).
Does Really High Quality Human Evidence On Intermittent Fasting Even Exist?
A very salient quote from a 2015 paper:
[W]hether fasting actually causes improvements in metabolic health, cognitive performance, and cardiovascular outcomes over the long term; how much fasting is actually beneficial; and where the threshold of hormesis resides (i.e., a balance between long-term benefit from fasting compared with harm from insufficient caloric intake) remain open questions. Unfortunately, the vast majority of human studies of a fasting intervention were weight-loss studies using single-arm, nonrandomized approaches or multiple intervention arms with no control.
For fasting to be more than a weight-loss fad, greater scientific rigor is needed from interventional trials than is found in the literature. Whereas enthusiasm for fasting is increasing, clinical relevance remains low because of insufficient human data, including almost nonexistent controlled trials
Intermittent Fasting And Diabetes-related Indicators
Despite similarities in body fat loss between intermittent fasting and continuous energy restriction, there is some evidence to suggest that those who engage in fasting experience greater reductions in insulin resistance, which is a very fascinating consideration.
A 2018 randomized trial published in JAMA following patients with T2DM over 1 year period showed that intermittent fasting is no more effective than continuous energy restriction at reducing A1C ( a marker of blood sugar control).
Benefits Independent Of Weight Loss
So many people think of intermittent fasting purely as a means to an end when it comes to weight loss, but a very exciting new study has shown that fasting may offer health benefits independent of changes in weight.
A 2018 study out of Cell Metabolism explored, for the first time through a controlled trial, if fasting had metabolic benefits independent of weight loss.
They used a specific time of fasting ( early time-restricted feeding – eating early in day to align with circadian rhythm – finished eating by 3pm) and found it improved insulin sensitivity and blood pressure and reduced oxidative stress.
Today’s article is another step towards a better understanding of the potential benefits of intermittent fasting on human health.
There are certainly areas of interest that exist in this subject area, but higher quality evidence will be required before more firm claims can be made.
If you enjoy fasting and it helps you support feeling and eating well, it may offer additional metabolic benefits.
We cannot say, however, it is a one stop shop to fix all of the world’s health problems.
Until next time,
Andy De Santis RD MPH