Methods of Fasting: A More Sustainable Alternative to Dieting

By Abby Vallejo, RD, CPT

The word “diet” can be triggering for many people. Whether you’ve had personal experience with this or not, often just hearing the word “diet” makes us think of hunger, deprivation and lack of satisfaction, possibly even punishment. The thing about diets is, they only work (if they work) when you’re on them. While a small percentage of people manage to lose weight and keep it off long term, the majority of people (80-95%) will gain back the weight, and more, after going off the diet. Surely there must be a better way!
It is important to know that for any new behavior or method to be truly impactful, it must also be sustainable. Which means that it has to become part of your lifestyle, and be something you can see yourself committing to for the long term, maybe for the rest of your life. Lasting change is something that we commit to day in and day out, becoming a more evolved and better version of ourselves in the process. So how do we set ourselves up for success? How can we lose weight sustainably, without the sense of denial and the high probability of just gaining it all right back once we’ve achieved our goal? My answer to this is to shift our approach from dieting – what we eat, to timing – when we eat. Let me explain.
There are many different diets out there, but the basic premise of dieting is reducing intake and eliminating certain types of foods, meaning our primary focus is on what we can’t eat, and portion sizes of what we can eat. When we focus on timing how we eat, we put the emphasis on when we eat. Why is this important? It all comes down to the way our bodies metabolize and digest food. Our digestive systems are still those of our ancestors from our hunter-gatherer days, who did not have the convenience of super markets, drive throughs and cupboards full of easy snacks. There were regular periods of fasting until food was found, and during those times we survived by burning our body fat, a process known as ketosis.
On the other hand, the process of burning carbs is called glycolysis. It is key to note that we cannot burn fat and carbs at the same time – only one at a time and when given the choice, our bodies will always prioritize the carbs. When we eat carbs (anything more than 50 grams at a time) this evokes an insulin response as we metabolize, and this insulin response lasts for about 12-13 hours – even if we do not eat again during that period. During this time we are in “storage mode”, and we cannot burn our body fat. Now, back in hunter gatherer days this was fine because we would usually have plenty of time between meals, allowing our bodies to switch back into fat burning mode once the insulin response period was done. However, as you can imagine, it is entirely possible and common in our modern lifestyle to eat carbs all throughout the day and never allow our bodies enough time to switch from glycolysis back to ketosis. Which means we aren’t giving our bodies the chance to burn stored body fat, and doing so repeatedly over time causes our ability to burn fat efficiently to become sluggish.
Once you know about insulin response, and that it lasts for 12-13 hours, you start to see why timing when you eat is so important. We are supposed to be switching back and forth between carb burning and fat burning mode on a regular basis for optimum health. But are we actually eating in such a way that allows our body to do so? You may have heard of intermittent fasting or carb fasting, which are timed styles of eating that allow carbs but also take insulin response time into account. Studies show that intermittent fasting not only can facilitate healthy weight loss and improve metabolism, but that it also helps decrease appetite and significantly improves insulin sensitivity, meaning better blood sugar control. It even has been found to lessen inflammation and to help clear out toxins and damaged cells from the body, which is a key step in preventing chronic disease.
A popular style of intermittent fasting or carb fasting is an 18:6, which means you fast for 18 hours of the day (water, coffee and tea are allowed) and then eat your meals in a 6 hour window. Or if you’re carb fasting – an alternative take on intermittent fasting that’s easier if you tend to get hungry all the time – you fast from carbs for 18 hours of the day, while protein and healthy fats are still allowed (or very low carb foods, which is less than 50 grams at a time), and then you have a 6 hour window in which to eat your carbs. The appeal with carb fasting is you can still eat whenever you’re hungry, but by not consuming carbs you’re still allowing your body to get into fat burning mode because protein and fat do not require an insulin response. These two approaches are also more gentle on your body than the traditional Keto diet, which not only has the added challenge of adherence due to its restrictiveness, but when done in long periods Keto can also cause hormone imbalances, especially in women.
It can take 2-4 weeks for your body to adjust to intermittent fasting, but research shows benefits linked to improved cognition, heart health, physical performance, obesity and tissue health. These approaches of timed eating styles are preferable to traditional diets like Keto because they help prevent metabolic disease such as pre-diabetes/diabetes and facilitate sustainable weight loss over time, while preventing muscle wasting and fatigue because they allow for the replenishment of muscle glycogen stores – which come from carbohydrates. Both approaches, intermittent fasting and carb fasting, help prevent the possible hormonal imbalances associated with strict, long term very low carb diets.
Note of caution:
Longer periods of fasting (24 hours or more) are not recommended – your body can go into starvation mode, making it very hard to lose weight
Fasting is not recommended for women who are pregnant or breastfeeding, for young children or those with eating disorders
Healthy, sustainable weight loss is approximately 1-2 lbs per week
Article: Cleveland Clinic Health Essentials. Oct 1 2019, Diabetes & Endocrinology. https://health.clevelandclinic.org/why-people-diet-lose-weight-and-gain-it-all-back/
Article: Harvard Health Staying Healthy. Nov 16 2021, Intermittent Fasting. https://www.health.harvard.edu/blog/intermittent-fasting-surprising-update-2018062914156
Journal: Cho, Yongin et al. “The Effectiveness of Intermittent Fasting to Reduce Body Mass Index and Glucose Metabolism: A Systematic Review and Meta-Analysis.” Journal of clinical medicine vol. 8,10 1645. 9 Oct. 2019, doi:10.3390/jcm8101645
Abby Vallejo, RD, CPT

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