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Does intermittent fasting offer any additional benefits for someone already on a Keto Diet?

Intermittent Fasting

Absolutely! For anyone following a ketogenic diet (KD), Intermittent Fasting (IF) is an excellent ‘add-on’ strategy that can have multiple health benefits beyond weight loss. Together, the KD and IF form an ideal combination for boosting weight and fat loss and overall metabolic health. Similar to the nutritional ketosis experienced on a KD, during the prolonged fasting period associated with IF, the body makes the ‘switch’ to using fatty acids and ketones as its main source of energy1. This ‘flip’ in the metabolic switch, called intermittent metabolic switching (IMS), can begin to occur as soon as 12 hours after you stop eating2.

NOTE: We wrote about IF and its multiple health benefits in our guest blogpost on Healthy Voyager – 5 Benefits of Intermittent Fasting for Keto.

We are strong advocates for a variation of IF called Timed Restricted Feeding (TRF), also referred to as Timed Restrictive Eating (TRE).

What is Time Restricted Feeding or TRF?

This form of IF involves daily fasting for a 12 to 20-hour interval (including sleep time!) and limiting food consumption to a 4 to 12-hour eating window of your choosing. This time-restricted eating method is the easiest to implement – it allows more scheduling flexibility and offers the most sustainable approach to IF. A subcategory of TRF, referred to as “early time-restricted feeding” (eTRF), has been gaining notoriety in the IF research community. True to its name, eTRF restricts eating to the early part of the day, prolonging the evening fasting interval.

What does the latest research on TRF/eTRF reveal about this very simple metabolic ‘hack’ for managing health?

TRF and eTRF can offer an additional boost to your blood sugar and metabolic health, above and beyond its effect on weight loss, by:

1. Boosting insulin sensitivity: TRF improves the whole body’s level of insulin sensitivity, including that of our body’s fatty tissue3. A high insulin sensitivity level allows our cells to use blood sugar more effectively. 

2. Improving beta-cell function: eTRF boosts the responsiveness of the insulin-producing cells (beta cells) of the pancreas by allowing a longer rest period between meals, which promotes the regeneration of these specialized cells4.

3. Reducing fasting and after-meal insulin levels: By lowering insulin levels, TRF can help manage the many diseases and health conditions associated with chronically high levels of insulin (hyperinsulinemia), such as diet-induced obesity, metabolic syndrome, type 2 diabetes, heart disease, and certain cancers5.

4. Reducing oxidative stress and inflammation: eTRF decreases levels of a biomarker in our body linked to cell membrane oxidation, helping to minimize cell damage and improving our body’s balance of antioxidants and free radicals. TRF also reduces levels of inflammatory compounds in our body that play a role in the progression of heart disease and type 2 diabetes6 7.

5. Taking the edge off evening hunger: eTRF decreases the desire to eat later in the day and promotes increased feelings of fullness in the evening, helping to curb food intake and facilitate weight loss.

6. Lowering blood pressure: Just as TRF has been shown to boost the body’s insulin sensitivity and lower insulin levels, this same effect has also been shown to dramatically lower blood pressure.

7. Decreasing levels of triglycerides and unhealthy cholesterol while boosting healthy cholesterol: TRF can not only lower the levels of blood fats (triglycerides) and the unhealthy LDL-cholesterol, but can also boost levels of the healthy HDL-cholesterol.

8. Strengthening our circadian rhythms: eTRF has been linked to a stronger alignment with the 24-hour ‘internal clock’ that runs in the background of our brain. Our physiology and our body functions are synchronized with these circadian rhythms, and, from a metabolic standpoint, appear to be enhanced when our food intake occurs earlier in the day8 There are a number of physiological processes that illustrate the harmony occurring between our body’s internal clock and our metabolic functions: Our body’s insulin sensitivity, beta-cell (insulin-producing) responsiveness, and the ‘heat producing’ effect of meal digestion are all higher in the morning than in the afternoon or evening; Both our rate of stomach emptying and blood flow are also greater during the daytime than at night; and, if you are being treated for high cholesterol, another potential motivator for making the switch to eTRF is that cholesterol synthesis is actually higher in the evening9.

Takeaway

For the prevention and management of metabolic conditions (such as type 2 diabetes), recent research highlights the importance of controlling not only what and how much you eat, but WHEN you eat. Time Restricted Feeding (TRF) and especially the early form of TRF (eTRF), which combines daily intermittent fasting (IF) and eating in alignment with our circadian rhythms in metabolism, have proven to be an especially effective form of IF. Simply changing the timing of your meals, by eating earlier in the day and extending the overnight fast, can significantly benefit your metabolism regardless of weight loss. For anyone following a ketogenic diet (KD), an 8 to 9-hour TRF regimen can easily be incorporated as a supplemental strategy to improve blood sugar, cholesterol, blood pressure, and hunger management, and to lower insulin levels and inflammation.

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  1. Flipping the Metabolic Switch: Understanding and Applying Health Benefits of Fasting https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5783752/
  2. Intermittent Fasting in Cardiovascular Disorders—An Overview: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6471315/
  3. Time-restricted feeding and risk of metabolic disease: a review of human and animal studies: https://www.ncbi.nlm.nih.gov/pubmed/24739093
  4. Early Time-Restricted Feeding Improves Insulin Sensitivity, Blood Pressure, and Oxidative Stress Even without Weight Loss in Men with Prediabetes: https://www.cell.com/cell-metabolism/pdfExtended/S1550-4131(18)30253-5
  5. Hyperinsulinemia: A unifying theory of chronic disease? https://diabesity.ejournals.ca/index.php/diabesity/article/viewFile/19/61
  6. Autophagy-induced degradation of Notch1, achieved through intermittent fasting, may promote beta cell neogenesis: implications for reversal of type 2 diabetes https://openheart.bmj.com/content/openhrt/6/1/e001028.full.pdf?ct=
  7. Effects of eight weeks of time-restricted feeding (16/8) on basal metabolism, maximal strength, body composition, inflammation, and cardiovascular risk factors in resistance-trained males: https://translational-medicine.biomedcentral.com/articles/10.1186/s12967-016-1044-0
  8. Intermittent Fasting and Human Metabolic Health https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4516560/
  9. Metabolic Effects of Intermittent Fasting  https://www.annualreviews.org/doi/pdf/10.1146/annurev-nutr-071816-064634
Mary Paley

Fearless Dietitian; 30+ years as a professional dietitian; Master’s Degree in Nutrition and Dietetics at the MGH Institute of Health Professions; Lead research dietitian for several major pharmaceutical companies; Currently focused on health and wellness and the benefits of ketogenic diets for both obesity and diabetes management. MS, RDN, CDE, LD/N

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