Recently, the protein-sparing modified fast has gained widespread popularity among dieters. However, very little evidence-based information is available on this diet, and most of the diets described are variations of each other.
The popularity of this diet is attributable to the significant amount of weight that can be lost during a short period of time. While the protein-sparing modified fast (PSMF) can help reach short-term weight loss goals, it’s highly restrictive and very low in calories. Thus, it carries a risk of nutritional deficiencies and weight regain (6).
What Does Protein Sparing Mean?
The term “sparing protein” does not necessarily mean that protein is better than other macronutrients; it refers to the diet’s main goal, which is to maintain muscle mass while losing fat.
In addition, to spare protein means that the diet provides adequate levels of essential amino acids to not impair the body’s ability to rebuild muscles and connective tissue (6).
A “modified” fast refers to a diet that is modified from other fad diets. This type of nutritional plan goes beyond simple caloric restriction for weight loss; it focuses on the quality and timing of food intake instead.
The principles of this diet are simple; calories are restricted so that your body uses mostly fats as fuel instead of burning muscle tissues, which can be used even when fasting or not eating enough calories from protein.
The protein-sparing modified fast allows just enough protein and carbohydrates to provide energy for normal daily activities but the rest should come from dietary fats and protein foods such as lean meat, poultry, eggs and seafood like fish. Since this diet is not complete, people should also take food supplements to prevent nutritional deficiencies.
How To Properly Do A Protein Sparing Modified Fast
A protein-sparing modified fast is a high-protein calorie-restricted diet combining several nutritional approaches including intermittent fasting, low-glycemic eating, and ketogenic eating.
The modified fast is designed to provide both the benefits of fasting and eating one’s favorite foods. A protein-sparing modified fast doesn’t necessarily eliminate carbohydrates entirely, but it does limit them substantially.
This semi-starvation approach promotes rapid fat loss while maintaining lean muscle tissue through increased secretion of growth hormone (GH). Even though many people believe that GH makes one “bulky” or causes unwanted body fat increase, research proves otherwise. GH actually spares fat stores by accelerating gluconeogenesis, a procedure that turns non-carbohydrate food sources into glucose to meet the needs of thyroids and other endocrine glands. As it is impossible to avoid gluconeogenesis while following this diet, there will be no decrease in muscle mass (7).
To ensure safe and effective weight loss using protein-sparing modified fast, one should eat moderately every day and create 12-14 hour daily fasting periods (7).
Although meals containing proteins are eaten regularly throughout the day, their amounts are restricted so that patients consume just enough calories to maintain substantial weight loss without feeling hungry during fasting hours.
Importantly, the protein-sparing modified fast should be implemented under professional guidance, especially for women and girls who want to lose additional body fat without experiencing related health disorders. The dieter is examined regularly to ensure that they lose only adipose (fat) tissue while preserving lean muscle mass and overall health.
One of the most critical aspects of this protocol is that all food must be eaten in small amounts throughout the day, thus making it impossible to overeat at one time.
In addition, meat products are consumed with every meal as they have been shown to promote faster weight loss compared with other types of food. However, all cooked foods should be thoroughly chewed before swallowing them, as eating in this manner helps lymphatic glands remove fats from food more effectively during digestion.
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Benefits Of The Protein Sparing Modified Fast Diet
Following a PSMF has been associated with several benefits, including:
The concept behind it is that by consuming only a very low amount of calories per day, patients will lose a significant amount of fat while keeping lean muscle mass untouched (6).
Furthermore, many people find it easier to stick to this protocol instead of traditional diets because they are allowed plenty of food options and can eat regularly throughout the day.
Improved Blood Sugar Control
Blood sugar control is another benefit of using the PSMF, especially for people with diabetes. Although it’s a semi-starvation diet, its low glycemic index makes it safe to use for both types I and II diabetics (1).
Promotes Healthy Thyroid Levels
Many people have been able to regulate their thyroid levels by following this protocol. As high levels of thyroid hormones are linked to obesity, this diet helps keep the body’s metabolism in check (3).
Minimizes Hunger Pangs
“Hunger pangs” is a term used for feelings of weakness and hunger that occur due to inadequate caloric consumption. As PSMF contains foods that are low on the glycemic index, it minimizes these feelings (3).
Decreased Cholesterol Levels
Research suggests that eating moderate amounts of protein, rather than high-carbohydrate foods, may significantly decrease total cholesterol levels (2).
Throughout the day, patients on this diet can eat as much meat and other protein sources as they desire while consuming smaller portions of non-starchy vegetables like broccoli, cauliflower, lettuce, etc. Most fruits are also acceptable to consume except for bananas and others high in sugar and starch. Berries (such as strawberries) are very good fruit choices for those following PSMF protocol since they have a low glycemic index and contain plenty of minerals and fiber (2).
Potential Risks Of The Protein Sparing Modifies Fast Diet
As with any diet, there are potential risks associated with following a protein-sparing modified fast diet plan.
One risk is that the low-calorie intake could lead to malnutrition. A person who chooses a PSMF should get adequate micronutrients, especially vitamins B and D (6).
Additionally, the diet could cause disordered eating; however, this can be minimized by closely following healthy routines around food and exercise (5).
As with any diet, it might be difficult for some people to adhere to. PSMF may fail at helping you lose weight in an acceptable amount of time. While there may be initial weight loss as water weight is lost, it may become unrealistic to lose large amounts of weight while still adhering to the diet (4).
This diet is not recommended for the following groups of people (6):
- Older adults
- People with a history of disordered eating
- Pregnant or breastfeeding women
- People with a BMI lower than 27
- People with a history of gallstones or have had their gallbladder removed
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The Protein Sparing Modified Fast Food List
Here are some of the foods you can eat as part of a PSMF:
- Poultry – skinless chicken, turkey, goose, and duck
- Meat – lean beef, pork, and lamb
- Seafood – any types of fish, but avoid shellfish
- Vegetables – almost all types (except for potatoes, corn, and carrots, and any starchy vegetables)
- Dairy – skim milk, cheese, cottage cheese, protein powders. Keep in mind that you may want to limit your dairy intake as it is high in fat.
A protein-sparing modified fast keto limits carbs and fats. Here are some foods you should avoid:
- Fruits – especially bananas, apples, pears, melons, and other fruits with lots of sugar
- Berries – especially strawberries in large quantities (I suggest eating only 1/4 cup a day)
- Grains – wheat, oats, barley, millet, quinoa, and buckwheat
- Legumes – black beans, lentils, kidney beans, peanuts, and chickpeas
- Processed foods and fast foods
- Artificial sweeteners and sweetened beverages
The Bottom Line
People who want to lose weight quickly while improving their overall health may find it helpful to follow the protein-sparing modified fast. It has been used for years by people seeking weight loss without losing muscle tissue or feeling hungry many hours a day.
Although many people find this semi-starvation approach to be highly restrictive and difficult to follow long-term, it can still be a safe and effective option for weight loss when performed under the guidance and supervision of a healthcare professional.
This article is intended for general informational purposes only and does not address individual circumstances. It is not a substitute for professional advice or help and should not be relied on to make decisions of any kind. Any action you take upon the information presented in this article is strictly at your own risk and responsibility!
- A Systematic Review of Evidence on the Use of Very Low Calorie Diets in People with Diabetes (2017, nih.gov)
- Effects of a short-term (4 weeks) protein-sparing modified fast on plasma lipids and lipoproteins in obese women (1990, nih.gov)
- Feasibility of protein-sparing modified fast by tube (ProMoFasT) in obesity treatment: a phase II pilot trial on clinical safety and efficacy (appetite control, body composition, muscular strength, metabolic pattern, pulmonary function test) (2013, nih.gov)
- The Effect of Starting the Protein-Sparing Modified Fast on Weight Change over 5 years (2020, nih.gov)
- The evolution of very-low-calorie diets: an update and meta-analysis (2006, pubmed.gov)
- The Protein-Sparing Modified Fast Diet. An Effective and Safe Approach to Induce Rapid Weight Loss in Severely Obese Adolescents (2016, nih.gov)
- Using a Revised Protein-Sparing Modified Fast (rPSMF) for Children and Adolescents with Severe Obesity: A Pilot Study (2019, nih.gov)