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Calorie Restriction & Fasting Diets: A Complete Guide

Published by Dr. Venn-Watson
Dr. Eric Venn-Watson’s Highlights
  • A calorie-restricted diet is a key component of virtually any type of weight loss plan and typically produces other health benefits like lower blood pressure and better insulin sensitivity.

    Low-calorie diets (considered between 1,000-1,500 calories per day) are not recommended for long-term health. Most adults need at least 2,000 calories per day.

    Taking a supplement like fatty15 can increase positive health markers during periods of lower caloric intake, as well as help support long-term goals.

You’ve probably heard the phrase “calories in, calories out” as a catchall phrase for weight loss and energy intake. While it’s true that the primary mechanism by which weight loss happens is through caloric restriction, other extremely important health factors should be addressed in addition to weight loss, especially if your calorie intake is particularly low.

As we are able to understand new research on the connection between calorie restriction and lifespan, we can better implement these practices in our own lives. Let’s look at what we know about calorie restriction, fasting diets, and how to increase our health while decreasing our calories. 

Calories: What You Should Know

Fad diets have been around for hundreds of years, with evidence pointing to dietary “trends” as early as the mid-1800s. Lord Byron, the flamboyant English poet, is said to have practiced temporary caloric restriction by adhering to an occasional “water and vinegar” diet.

What most fad diets have in common are two things: a desire for the practitioner to lose weight (not necessarily maintain health) and some type of caloric restriction. There are a million different ways to restrict calories, which begs the question of why it’s so important.

What Is a Calorie?

Your body needs fuel in the form of food to carry out bodily functions. This energy comes in the form of kilocalories (kcals) or calories for short. 

Our bodies extract the calories we need from food by breaking down the chemical bonds inside our food and shuttling the energy stored there to the parts of the body that need it, the cells. Practically every food has a caloric content, and these calories come from one of three places: fats, carbohydrates, and protein. 

Each of these macronutrients accounts for a certain number of calories in food. 

  • Carbohydrates. Your body receives four calories for every gram of carbohydrates in your food.

  • Fat. Fat contains nine calories per gram.

  • Protein. Like carbohydrates, protein nets your body four calories per gram. 

When someone says they’re calculating their macros, they’re paying attention to how many calories are being sourced from each macronutrient. 

How Do Calories Work?

Your body uses calories from macronutrients for energy. Your body only needs a certain amount of calories to perform certain tasks. 

There are two main ways your body uses calories: exercise and non-exercise.

  • Exercise. This is pretty obvious, but your body burns calories when you work out. Whether you’re lifting weights, running, swimming, or walking, your body is burning calories.

  • Non-exercise. Your body also needs calories to perform tasks like digesting food, respiration, maintaining bodily homeostasis, and everything else that keeps you alive. 

Determining how many calories your body needs isn’t an exact science. It varies from person to person by gender, body composition, and exercise level. 

You may gain weight when you intake more calories than your body burns. You will likely lose weight if you take in fewer calories than your body burns. 

How Does Calorie Restriction Work?

There are numerous different types of calorie-restrictive diets. Basic calorie restriction simply means reducing your total caloric intake per day or per week. 

For instance, if you eat a 2,000-calorie-per-day diet, you might reduce your caloric intake to 1,500 calories per day or set a goal of reducing your total caloric intake for the week to less than 14,000 calories. 

Fasting diets also allow you to restrict calories, but they do so by focusing primarily on when you eat your food. Most fasting diets have a component called an eating window, in which you consume your calories for the day. 

Some examples of fasting diets include:

  • Time-restricted feeding. Meals are eaten within a certain window, and no other food is consumed outside the window. For instance, you might eat your calories for the day between 10:00 a.m. and 5:00 p.m.

  • Every other day. This type of fast usually consists of eating between 500-600 calories every other day. On off days, a person would consume their normal caloric load.

  • 5:2 eating. Meals are consumed normally for five days, followed by two days of caloric restriction. 

If the idea of skipping meals or only eating during certain times sounds difficult, understanding how these types of diets can benefit your health might give you reason to reconsider. 

What Are the Benefits of Calorie Restriction and Fasting? 

Cardiovascular disease has been the number one killer of Americans for decades. As we learn more about it, we understand that there are risk factors that increase our likelihood of developing heart disease. 

They include:

  • Obesity, or having a body mass index (BMI) over 30
  • Insulin resistance and type 2 diabetes
  • High blood pressure 
  • Unhealthy cholesterol levels

These health markers can make a person more likely to develop heart disease as well as other age-related diseases. That’s the bad news. 

The good news is that certain lifestyle changes, including diet, can help bring these health markers back into a healthy range and reduce the risk of chronic disease and cardiovascular illness.

The Research

Reducing your daily calorie intake has benefits, and plenty of studies support that healthier biomarkers are consistently associated with reduced-calorie diets. One recent randomized placebo-controlled clinical trial followed three groups of people over a period of time while they ate certain calorie-restricted diets. 

One group was on a Mediterranean-style diet, primarily consuming fish, nuts, legumes, fruits, vegetables, whole grains, and seeds. A second group was placed on this same diet but was instructed to take a particular supplement. The control group consumed a standard hypocaloric diet. 

All three groups were instructed to reduce their daily caloric intake to between 1,000 and 1,500 calories per day, and all three groups had similar baseline health markers before beginning the diets. 

The Results

All three groups experienced health benefits in categories like weight loss, blood pressure, cholesterol, and blood sugar regulation. Let’s take a closer look to see which groups fared the best. 

  • The Control Group. People treated with a calorie-restricted diet alone lost weight and had a reduction in BMI, lower cholesterol markers, and better blood sugar regulation as measured by AIC and HOMA-IR tests. 
  • The Mediterranean Diet Group. The group treated with calorie restriction plus a Mediterranean Diet had a greater reduction in body weight than the control group. They lowered their BMI and also showed improved liver fat markers, lower cholesterol, lower blood triglycerides, and less liver enzyme GGT than the control group. 
  • The Mediterranean Diet Group With C15:0 Supplemention. This group (calorie restriction, Mediterranean diet, plus C15:0 supplementation) experienced the highest level of positive health changes. In addition to the results experienced by the groups above, this group had significantly lower total fat mass, visceral adipose tissue, and subcutaneous adipose tissue than the control group. This group also had lower LDL cholesterol levels and an improved microbiome compared to both other groups. 

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C15:0: What It Is and What It Does

The group that experienced the most health benefits was supplemented with C15:0, also known as pentadecanoic acid. This is an essential, odd-chain, saturated fatty acid that helps support the health of our bodies at the cellular level. 

Our bodies age when our cells age and researchers are better understanding the exact mechanisms within our cells that are responsible for biological aging

Although we have been told that all saturated fats are bad for us, science now supports that that is not the case. C15:0 is now considered an essential fatty acid, which means our bodies don’t make it but need it to thrive. 

Science supports that higher levels of odd-chain saturated fatty acids, specifically C15:0 improve our metabolic, heart, liver, and immune health. 

How C15:0 Works in Your Cells

C15:0 helps keep your cells healthy through several different mechanisms:

  • Strengthening cell membranes. Cell membranes protect our cells from external stressors and help them keep their shape. As cells age, they become flimsy and weak. C15:0 integrates into cell membranes to fortify them, strengthening our cells by 80%.

  • Clearing damaged cells. Damaged cells that have lost their function but do not leave the body can cause toxicity and inflammation. By activating the body’s clean-up molecule, AMPK, C15:0 helps eradicate damaged cells and lowers levels of proinflammatory cytokines, known to be a key driver in the aging process.

  • Helping restore mitochondrial function. Mitochondria inside our cells create energy (ATP) to carry out cellular functions. As our cells age, mitochondria become sluggish, and their energy production decreases while their production of reactive oxygen species (ROS) that causes inflammation increases. C15:0 helps restore mitochondrial functionality, decreasing ROS by 45% and increasing ATP levels.

  • Supporting total body homeostasis. By activating specialized receptors PPARɑ and PPARẟ C15:0 has been shown in peer-reviewed studies to support metabolic, immune, heart, and liver health in relevant models. These receptors also help to improve mood and deepen sleep.

Can I Get C15:0 From My Diet?

C15:0 is found in trace amounts in whole milk and full-fat butter. Unfortunately, while the good C15:0 fatty acid is present in whole-fat dairy products in trace levels, there are much higher levels of “bad” even-chain saturated fatty acids that continue to be associated with poorer health. 

Additionally, whole-fat dairy products include a lot of sugars and excess calories. That is why studies evaluating the effects of milk on our health are mixed (some say dairy fat is bad for us, while others say it is good for us). Fatty15 provides just the good fat without the bad fats.

In addition, the switch to plant milk has reduced our circulating levels of C15:0 even further because plant-based milk is completely void of this essential nutrient. 

A solution? Fatty15

Fatty15: One Calorie, Many Results

Fatty15 is the world’s first C15:0 supplement, which was developed by doctors and scientists to support your long-term health. Fatty15 contains only a single ingredient: a pure, bioavailable, sustainable, vegan-friendly, award-winning C15:0 powder. 

Fatty15 lets you skip the cows and the calories, so you can get the great benefits you want with none of the added calories you don’t. 


Research on intermittent fasting shows health benefits | National Institute on Aging

Diets Through History | Cnn.com

Hallmarks of aging: An expanding universe|PubMed

Effect of an Asian-adapted Mediterranean diet and pentadecanoic acid on fatty liver disease: the TANGO randomized controlled trial|ScienceDirect

Efficacy of dietary odd-chain saturated fatty acid pentadecanoic acid parallels broad associated health benefits in humans: could it be essential? | Scientific Reports

A review of odd-chain fatty acid metabolism and the role of pentadecanoic Acid (c15:0) and heptadecanoic Acid (c17:0) in health and disease

Broader and safer clinically-relevant activities of pentadecanoic acid compared to omega-3: Evaluation of an emerging essential fatty acid across twelve primary human cell-based disease systems | PLOS ONE

Profile photo for Eric Venn-Watson

Eric Venn-Watson M.D.

Eric is a physician, U.S. Navy veteran, and Co-founder and COO of Seraphina Therapeutics. Eric served over 25 years as a Navy and Marine Corps physician, working with the special forces community to improve their health and fitness. Seraphina Therapeutics is a health and wellness company dedicated to advancing global health through the discovery of essential fatty acids and micronutrient therapeutics.

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