Does Intermittent Fasting Speed Up Weight Loss?
Intermittent Fasting 101
Intermittent Fasting (IF) has had a surge in popularity lately as one of the hot “new” health and diet trends. So what’s all the fuss about? Many studies show that it can have powerful effects on your body and brain, and may even help you live longer. But will it help you lose weight? How do you do it? Here’s a breakdown of IF, what the benefits and drawbacks are, different styles, and the most common questions answered!
What is Intermittent Fasting?
Intermittent Fasting is essentially just a time-restricted eating pattern in which you cycle between periods of eating and fasting. It doesn’t have rules about what you should eat, or how much, but rather just dictates WHEN you eat (so it’s more of an eating pattern than a “diet”). The concept of fasting isn’t new, and many will point out that fasting has been common throughout human evolution - from our hunter-gatherer days to religious and spiritual practices.
There are different “styles” of IF in which you fast for certain amounts of time or on certain days. While there are several variations, the most common intermittent fasting methods involve 16 hours fasts (thereby eating during an 8 hour window), or doing a true fast for 24 hours 1-2 times per week. The 16/8 method is the easiest to maintain for most people - and particularly active people - because it’s consistent every day.
How does it work and what happens in your body when you fast?
There are many things that happen in your body when you fast, on cellular and molecular levels:
- Human Growth Hormone (HGH) level skyrocket as much as 5 times their norm, which can have benefits for fat loss and muscle gain.
- Insulin Sensitivity improves and insulin levels drop, which makes stored body fat more accessible.
- Cellular Repair: When fasted, your cells initiate important repair processes.
- Gene Expression: Genes that function to help with longevity and protection against disease activate.
What are the Benefits?
Here are the main health benefits of intermittent fasting:
- Insulin resistance: IF can reduce insulin resistance, lowering blood sugar and fasting insulin levels, which can protect against type 2 diabetes.
- Inflammation: Some studies show reductions in markers of inflammation, a key driver of many chronic diseases.
- Heart health: IF may help reduce “bad” LDL cholesterol, blood triglycerides, inflammatory markers, blood sugar, and insulin resistance — all risk factors for heart disease.
- Cancer: Animal studies have shown that IF may prevent cancer.
- Brain health: IF increases the brain hormone BDNF and may aid the growth of new nerve cells. It may also protect against Alzheimer’s disease.
- Anti-aging/longevity: Intermittent fasting can extend lifespan in rats. Studies have shown that fasted rats lived 36–83% longer.
- Weight loss: This is the controversial one. IF can help you lose weight and belly fat, without having to consciously restrict calories by just giving you strict guidelines to get your food in (and perhaps curb late night snacking, for example). BUT this is not a side effect of the time-restricted eating, but rather being in a caloric deficit, as is required for all weight loss methods to be effective.
- Simplicity: This method of eating is pretty simple, and black-and-white.
While there has been an increasing amount of research on the topic of fasting, keep in mind that many of the studies were conducted with animals, and the human studies have been done only for limited time periods and with overweight, middle-aged populations, so we should have more information once we have a wider variety of quality human studies in the mix.
What are the Drawbacks?
- Weight Loss? Maybe: As we mentioned above, IF is often marketed as a “diet” or weight loss program… It is not that; it is an eating pattern. IF does NOT lead to weight loss. It CAN possibly aid in weight loss, but at the end of the day, weight loss comes from being in a caloric deficit - NOT from time-restricted eating. Can time-restricted eating help you eat in a caloric deficit? Sure, but it’s not inherently going to cause you to lose weight.
- Harmful to some populations: IF is NOT a good option if you’re underweight or have a history of disordered eating, as it could be harmful.
- Less clear on the benefits for women: There is some evidence that intermittent fasting may not be as beneficial for women as it is for men. One study showed that it improved insulin sensitivity in men, but worsened blood sugar control in women. Additionally, there are reports of women whose menstrual period stopped when they started doing IF and went back to normal when they resumed their previous eating pattern. So if you’re trying to conceive, having difficulties with fertility, pregnant, or breastfeeding, this isn’t going to be the best option for you - and we will anxiously await more information and human studies on the topic.
- Socially complicated: This isn’t the societal “norm” when it comes to eating the typical 3 meals per day with some snacks, so it can be socially tricky to navigate at times - like when others are eating/drinking and you are deliberately not due to a fast.
- Adjustment period: IF can be difficult to adjust to a time-scheduled eating pattern. Upon implementing, some people find themselves hungry, light-headed, dizzy, and/or with an inability to concentrate or perform well mentally and physically - particularly in the first month or two as people adjust to the new eating style. Many encourage a gradual implementation, expanding the fasted timeframe slowly over a few months.
- Can I drink liquids during the fast? Water is fine… it’s anything with calories that’s up for debate. Technically anything besides water will break your fast, but many will say that water, coffee, tea, or other low/non-caloric beverages (less than 50 calories, and no sugar added) are fine, and even allow for small amounts of milk or cream. Some argue that coffee is especially beneficial because it can blunt hunger, and that having a little beverage to help you keep your fast is preferable to breaking it completely with food.
- Should I work out in a fasted state? Or how should I organize my training schedule around a fast? It may take some getting used to, especially if you’ve never worked out fasted, and you might need to play with your training schedule to find something that works well for you. Preferably, you’re eating your biggest meal within an hour or two after training. Some argue that BCAAs, while they will break your fast, will allow for better training adaptation and less muscle loss/more muscle gain.
- When does the fast technically start? When you’re finished eating your last meal, that’s when the clock starts.
- Does this mean I can eat whatever I want during the eating window? While IF doesn’t have any “rules” about what you can and can’t eat (only when), what you eat and how much will play a massive role in the outcomes you see.
Like all “diets”, Intermittent Fasting has its benefits and drawbacks, and we are constantly learning more about this method as we see more research come out. Hopefully this clears up some of the details of this trendy diet for you, and, as always, obviously consult a qualified nutrition professional and/or doctor to see if this might be a good option for you!