IN CURRENT DIETING TERMS, FASTING INVOLVES PURPOSEFULLY NOT EATING OR MARKEDLY RESTRICTING FOOD INTAKE AND ONLY DRINKING BEVERAGES like water, black coffee, and unsweetened tea.
Intermittent fasting (IF) defines a number of different types of willing behaviors that also require abstaining from food for specific periods of time of the day or days of the week. According to a Wikipedia entry (chosen as a reference for this post because the item explains, rather than promotes, defends, or criticizes, the practice in common terms) there are several types of IF: alternate day, periodic, and time restricted (most popular).
Numerous online posts discuss the pros and cons of IF. A longer scientific article that explains IF is available through this PubMed link: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5783752/
This Earned Runs post isn’t about the merits or effectiveness of not eating food but discusses a recent topic that has surfaced concerning allowed beverages. A June 2019 post on soberalley.com, “fasting + fitness for women” that was updated in early November 2019 takes on the subject of DIRTY V CLEAN intermittent fasting.
The post, “What Can I Drink While Intermittent Fasting” provides a lengthy discussion of “dirty” versus “clean” time-restricted IF in easy to understand terms.
Clean fasting, when it comes to beverages the piece explains, only allows ingestion of unflavored, unsweetened water, coffee, and tea during food-restricted hours. Dirty fasting loosens these restrictions and allows non-calorie beverages, non-sugar sweetened gum, and a small amount or “splash” of cream. The rationale behind the relaxation is that if lowering daily calorie intake to achieve weight loss is the goal of following such a regimen, adding non-calorie drinks should be okay. Especially if the inclusion makes fasting less odious and increases the likelihood of adherence.
However, this reasoning does not take into account the role of insulin in weight control, the article importantly informs readers. Or body composition, it seems.
As a response to sugar intake, after subsequent breakdown and absorption by the digestive tract as glucose into blood (blood sugar spike after a meal), the pancreas releases insulin into the bloodstream. Insulin helps move glucose from blood into tissues where it can be utilized as energy or stored as fat. When blood glucose levels need boosting, other hormones act to stimulate breakdown of glycogen in the liver (glycolysis) into glucose, and the synthesis of new glucose (gluconeogenesis) from other materials including those derived from catabolism of body structure protein (like in muscle and bone).
To athletes this means traditional, continuous calorie restriction dieting that does not include 12-pus hour fasts may lead to intervals in which these important tissues are broken down to be used to make glucose for fuel.
During a FASTING period of at least 12 hours duration, in the absence of food intake, blood glucose/sugar levels decrease. Because an insulin response is not stimulated during the fast, stored body fat is broken down to components (fatty acids and fatty acid-derived ketones) which can serve as a substitute energy source, indicates the 2017 publication in the journal Obesity (referenced earlier) explaining the health benefits of fasting.
This “metabolic switch”, the authors say, from glucose as fuel to fatty acids and ketones, is flipped after about 12 hours in order to “sustain the function of muscle and brain cells during fasting and extended exercise.” Research findings are increasingly showing, they say, that these fat-derived substances appear to be the “preferential fuel for both brain and body” at such times and act to preserve lean muscle mass, and even increase exercise endurance!
Insulin inhibits the breakdown of body fat stores (lipolysis) for this purpose and prevents the switch from glucose to fat as fuel!
While there are well proven risks of fasting, most harmful effects have been experienced by persons fasting for several weeks or longer and not by those on short-term, intermittent fasts.
The scientific article goes into great depth explaining the beneficial physiological effects of IF on muscle, liver, brain, cardiovascular system, and blood biomarkers of inflammation and oxidative stress (thought to be anti-aging effects). Changes include lower blood glucose levels, increased insulin sensitivity, and improved exercise efficiency and cognition, for example.
Most of these metabolic and health benefits, the scientist authors say, are thought to be “driven by reductions in weight and/or body fat” accomplished through lipolysis during IF, or what most of us commonly refer to as “fat burning”!!!
This metabolic switching, with preservation of lean muscle mass and burning of fat, has special importance to older populations dieting to lose weight for medical reasons. They are already at risk of sarcopenia due to aging changes. The muscle preserving action of IF compared with traditional continuous calorie restriction regimens may allow safe weight reduction in this group, the article proposes.
In the DIRTY versus CLEAN INTERMITTENT FASTING (soberalley.com) article the topic of artificial sweeteners comes up, which links to references for those who wish to check the popular website sources of the statements made (Diet Doctor.com weight loss advice, HealthLine.com and Diabetes.co.uk) about Sucralose, Stevia, and erythritol-based sweeteners.
So, what about non-sugar sweeteners? If they do not contribute calories to the diet (the reason they are called “non-nutritive”), can zero-calorie products containing them be consumed during fasting, especially if the purpose of the fast is calorie reduction? Do artificial sweeteners have the same lack of metabolic effect on intermittent fasting as water?
Some non-sugar sweeteners (sucralose, possibly saccharin and acesulfame) stimulate the release of insulin! Why is this important? Because insulin BLOCKS the flipping of the “metabolic switch” from glucose to fat burning for fuel.
How? The taste in the mouth provided by such non-nutritive sweeteners triggers what scientists refer to as the Cephalic Phase Insulin Release (CPIR).
In one study, the insulin response to ingestion of sucralose in solid foods (gelatin cubes) seemed to be more significant in a subset of overweight and obese study participants compared to its ingestion in beverages. Other research suggests insulin sensitivity may decrease over time with chronic use, one of the metabolic abnormalities associated with type 2 diabetes.
After wading through some of the many recent research articles on the topic, I couldn’t find answers to all my questions about non-sugar sweeteners’ effect on fasting. Reading more raised more questions. If the sight, smell, tasting, chewing and swallowing of food are by definition part of the CPIR, must all these everyday pleasures be avoided to prevent insulin release and allow flipping of the metabolic switch?
By the end of a couple days of investigating dirty fasting my head was spinning. I was ready to give up searching and begin formulating a plan to re-work the personal IF program I had started this fall 2019. I started it mostly for its health benefits (anti-aging, preservation of muscle and bone, and brain health) and only a little for weight maintenance purposes.
I realized I had been dirty fasting. Really dirty. I drank multiple diet beverages a day (3-4), chain-chewed sugar-free gum, and sweetened several tea and cocoa drinks each day with sucralose. But I avoided all simple sugars (except for those in whole fruits).
I decided to base my IF program going forward on a few common-sense principles rather than the multiple, confusing and sometime contradictory science factoids unearthed during my search:
That’s one perspective on whether to clean or dirty fast based on my personal goals.
The soberalley.com article’s author (not identified) lays out several other logical options and approaches to clean vs dirty fasting. The author’s personal experiences are recounted and form the basis for the advice given to readers. Check it out for an easy read. Importantly it and other pieces on the topic raise awareness that potential metabolic effects of non-nutritive sweeteners may not be healthy for all, under all circumstances.
Life without diet soda and gum chewing is rough but I’m giving it a try and looking forward to a Thanksgiving weekend splurge!
RUN & MOVE HAPPY!
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5634742/ CPIR humans to sucrose and sweeteners
http://siimland.com/what-breaks-a-fast-while-intermittent-fasting/ another pop rticle?
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Running, walking, and fitness activities enable us to experience our physical selves in a world mostly accessed through use of fingers on a mobile device.
EARNED RUNS is edited and authored by me, runner and founder. I began participating in road races before 5Ks were common. I've been a dietitian, practiced and taught clinical pathology, and been involved with research that utilized pathology. I am fascinated with understanding the origins of disease as well as health.
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