[Huberman] Effects of Fasting & Time Restricted Eating on Fat Loss & Health


Health effects:

  1. Weight Loss: Fasting can lead to weight loss as it often results in a reduction of calorie intake. During fasting periods, the body may also shift to using stored fat for energy, which can contribute to fat loss.
  2. Muscle Maintenance: The impact of fasting on muscle maintenance can vary. Some fasting protocols, when combined with resistance training and adequate protein intake, may help preserve muscle mass while losing fat. However, prolonged or extreme fasting without proper nutrition can lead to muscle loss.
  3. Organ Health: Fasting can have beneficial effects on various organs. For example, it can improve gut health by giving the digestive system a break. Liver health may also benefit from fasting, as it can reduce the accumulation of fat in the liver and improve its metabolic functions.
    1. Increased insulin sensitivity, which is beneficial as type two diabetes is characterized by a reduction in insulin sensitivity
    2. Improvements in beta cell function in the pancreas.
    3. Decreased blood pressure.
    4. Decreased oxidative stress.
  4. Cognition: Fasting has been associated with improvements in cognitive function. This may be due to a variety of factors, including reduced inflammation, increased production of neurotrophic factors that support brain health, and the potential for fasting to promote autophagy, a cellular cleanup process that can clear out damaged components in cells, including neurons.

Hormones affected:

  1. Insulin. Time-restricted feeding seems to improve overall insulin profiles, which can lead to increased insulin sensitivity. This is beneficial because it can help prevent or manage conditions like type 2 diabetes, which is characterized by reduced insulin sensitivity.
  2. Testosterone. The study mentioned indicates that TRF, when calories are consumed within an eight-hour window as opposed to a larger feeding window, can lead to significant decreases in free testosterone. Free testosterone is the bioactive form of the hormone that exerts effects in the brain and body.
  3. Stress hormones and inflammatory markers. The 2012 Satchin Panda study on mice suggested that TRF could reduce them. This finding seems to be supported in humans as well, indicating that TRF can be compatible with quality hormone health.
  4. Despite some of the positive effects on hormones, the context suggests that for those who are training hard regularly, it is not advisable to restrict the feeding window to less than eight hours, as this could potentially have negative effects on hormone health.

Common TRF schedules:

  1. 16/8 Method: This is one of the most popular TRF schedules. It involves fasting for 16 hours and eating all meals within an 8-hour window. For example, if you finish dinner by 8 PM, you would not eat again until 12 PM the next day.
  2. 14/10 Method: This schedule is slightly less restrictive, with a 14-hour fasting period and a 10-hour eating window. For instance, if you finish eating by 7 PM, you can have your next meal at 9 AM the following day.
  3. 12/12 Method: This is a balanced approach where you fast for 12 hours and eat within a 12-hour window. This might be a more manageable starting point for those new to TRF, as it typically just involves not eating after dinner and skipping late-night snacks.
  4. One Meal a Day (OMAD): OMAD is an extreme form of TRF where all daily calories are consumed in a single meal, resulting in a 23-hour fast. This approach is not recommended for everyone and should be approached with caution.
  5. Alternate-day fasting: This involves eating normally one day and either completely fasting or significantly reducing calorie intake the next day. This is not a daily TRF schedule but rather an intermittent fasting approach that some people use.
  6. 5:2 Diet: Another form of intermittent fasting, the 5:2 diet involves eating normally for five days of the week and restricting calories to about 500-600 on the other two days. Again, this is not a daily TRF schedule but is related to the concept of restricted eating periods.

It's important to note that the specific time window for eating should ideally align with your active phase, typically during daylight hours, to reinforce the natural circadian rhythm. Consistency is also key; shifting the eating window frequently can disrupt the circadian clock and negate some of the benefits of TRF. "Perfect diet" for an individual on a given day is contextual and depends on what you did the previous day and what you plan to do the next day

The research suggests that for most people, especially those who are physically active, a minimum eating window of 8 hours is recommended to support hormone health and recovery needs.

Key mechanisms that are affected by TRF:

  1. Circadian Rhythms: TRF aligns food intake with the body's natural circadian rhythms, which are the physical, mental, and behavioral changes that follow a 24-hour cycle. Eating within a set window can help synchronize these rhythms, which can improve metabolism and overall health.
  2. Metabolic Switching: During the fasting periods in TRF, the body switches from using glucose as its primary source of energy to using fatty acids and ketone bodies. This metabolic switch can lead to improved insulin sensitivity, reduced inflammation, and other health benefits.
  3. Hormonal Regulation: TRF can influence the levels of various hormones related to hunger and satiety, such as ghrelin and leptin. By controlling the timing of food intake, TRF can help regulate these hormones, potentially reducing overall calorie intake and aiding in weight management.
  4. Cellular Pathways: TRF can activate certain cellular pathways that are involved in cell growth and repair. For example, fasting states can activate AMP-activated protein kinase (AMPK) and sirtuins, which are associated with cell repair and autophagy (the body's way of cleaning out damaged cells). On the other hand, feeding states can activate pathways like mTOR, which is involved in cell growth.
  5. Blood Glucose Levels: TRF can help stabilize blood glucose levels by limiting the intake of food to periods when the body is best prepared to handle it. This can be particularly beneficial for individuals looking to manage their blood sugar levels and reduce the risk of type 2 diabetes.
  6. Autophagy: During periods of fasting in TRF, the body can increase the rate of autophagy, which is the process by which cells break down and remove damaged proteins and organelles. This cellular "housekeeping" is crucial for maintaining cellular health and preventing diseases.