When it comes to very low calorie diets, they are an option here at Lifestyle Medicine Maine, but they are not the best option for most of us. A very low calorie diet involves intentionally restricting calories, but by how much and for how long? What does the evidence say? What are the risks?
VLCD's typically range from 800 kcal/day to as little as 400 kcal/day. If that sounds like very few calories, it is! To put this in perspective, most of us can maintain our goal weight consuming anywhere from 1,800 to 2,400+ calories per day (depending on age, muscle mass and activity level). A moderate calorie deficit is in the ballpark of 1,200 to 1,800 kcal/day -- but this really depends on where our starting weight is.
"Very low-calorie diets (VLCD) are hypocaloric dietary regimens of approximately 400–800 kcal/day that result in 20–30% reductions in body weight, sometimes in just 12–16 weeks" (1).
Contrary to popular belief, the use of VLCD's are well documented for their success. Over the past decade, VLCDs have been used extensively to show that the underlying cause of Type 2 Diabetes (insulin resistance) can be reversed with sufficient calorie restriction and weight loss. In fact, all of the major trials demonstrating reversibility of Type 2 Diabetes use a formula diet replacement (meal replacement shake) + non-starchy vegetables to get people there. If you want to explore these studies, then head over to my course on Reversing Prediabetes and Type 2 Diabetes.
Typical rates of weight loss on VLCD's vary by how much weight we have to loose, typically exceeding 2+ lbs per week. That said, most of us will experience a quicker weight loss during our first week as glycogen stores become depleted (glycogen in muscles stores water, so this isn't true fat loss).
For patient's requesting to pursue a VLCD, it is typical for clinics to use a complete meal replacement shake. Here at Lifestyle Medicine Maine, we do this better, with real food. We prescribe whole foods throughout this intervention and provide specific details and added support to help you succeed. Many patient's choose to pursue this option for anywhere from 1 day to 8-12 weeks. This duration depends on our starting weight and how we feel while following this program.
What is a typical macro-nutrient distribution range for a VLCD? While most of us do not need to focus on our protein intake when following a moderate caloric restriction, but VLCD's are different. We do need to make sure that we are consuming adequate protein and micronutrients when following a VLCD.
The Recommended Daily Amount (RDA) for protein is the amount needed to exceed the protein requirement for 98% of us (meaning that most of us will be consuming more protein than we need at that amount) (2, p536). The RDA for women after 19 years of age is constant at 46 grams/day of protein (2). While, by definition, this amount will provide more protein than half of us need, I prefer to err on the side of caution, aiming for 56 grams/day. This amount is more than adequate for 99% of us (exceeding the RDA by 20%). The rest can be divided between carbohydrates and fat with a focus on including as many whole plant foods as we can to optimize satiety and our micronutrient intake.
What are the downsides? VLCDs do come with risks which is why medical monitoring and blood tests is necessary:
Very low calorie diets (VLCDs) work well for those of us who are very regimented
VLCDs can lead to binging behaviors, especially if we don't consume adequate fiber.
Gallstones can occur, especially if the VLCD does not contain adequate dietary fiber (inflamed gallstones often require emergent abdominal surgery to remove)
Cases of pancreatitis have been reported
We need to use a nutritionally adequate plan. In the 1960's and 1970's, meal replacement shakes were not nutritionally adequate and lead to electrolyte imbalances (causing abnormal heart rhythms and deaths). A protein shake is not an adequate replacement. While I prefer to use whole plant foods, total meal replacement shakes do exist, but still need to be consumed with non-starchy vegetables (fiber) to keep our gut happy.
Alterations in Sodium, Potassium and Magnesium can occur, which is why we monitor lab work. Abnormal/low kidney function is a contraindication. If our eGFR is less than 30, then this is not recommended.
Dehydration if inadequate fluids are consumed
Increased risk for gout flares (as uric acid levels change)
Additional contraindications (reasons that this would not be recommended): recent myocardial infarction (heart attack); a cardiac conduction disorder; a history of cerebrovascular (stroke), or hepatic (liver) disease; cancer; type I diabetes; or unstable mental health condition
Protein-calorie malnutrition is possible if the calorie restriction lasts too long, especially if we do not focus on adequate protein intake.
Many prescription medications often need to be significantly titrated or abruptly stopped on day one or during the first week of a VLCD which is why close medical monitoring is critical. For example, people often experience a rapid drop in blood sugar and blood pressure (into the normal range), and so continuing with these medications could lead to overmedication and a medical emergency.
Pursuing a very low calorie diet could land you in the hospital.
Why even discuss VLCDs given the risks? It is important to understand the risks, as there are very serious risks involved. This option requires a high amount of commitment, medical supervision (typically including lab work every 1-2 weeks), frequent check-in's and added support. It is worth repeating that this is not the best option for most of us. Some of the risks are not predictable.
In the Evidence Based Weight Loss course, I share how I lost the last 10 lbs using a modified VLCD. I chose this option because the last 10 lbs are often the most difficult to lose. I also wanted to better understand how to practically leverage calorie density to increase satiety (fullness) while significantly cutting back on calories using real whole foods. It was surprisingly easy for me to follow -- but that was just my experience. Your experience may be different. While the allure of rapid weight loss is strong, this reward always needs to be balanced against the potential risks (listed above).
What do I think? Very low calorie diets are an option, but they are not the preferred option, and they do come with significant risks, which is why medical supervision is recommended. A thoughtful transition toward a plant predominant dietary pattern is a better option -- We need to develop the skills that we will need to maintain our weight loss long-term, and a gradual transition confers both weight loss and skill. That said, once we have built these skills, we may choose to accelerate our weight loss using small bursts of a VLCD -- it's up to you! I also understand that sometimes medication side effects can be intolerable and this can significantly motivate us to want to move quicker. Whatever your situation is, know that I am here to support you.
If you are looking to pursue a very low calorie diet, then make sure to request medical supervision through Lifestyle Medicine Maine. Once we've confirmed that you are a candidate, and you fully understand the risks involved, we can get started. Throughout this journey we'll perform screening labs every 1-2 weeks, titrate medications and monitor closely for potential complications. If this is something that you truly want to pursue, then I am here to help make this as safe as possible.
References
Remission of Type 2 Diabetes with Very Low-Calorie Diets —A Narrative Review. Juray et al. Journal Nutrients. (2021) https://www.mdpi.com/2072-6643/13/6/2086
Dietary Reference Intakes: the Essential Guide to Nutrient Intakes. The National Academies of Sciences. (2016) https://nap.nationalacademies.org/read/11537/chapter/59
Examination of whether early weight loss predicts 1-year weight loss among those enrolled in an Internet-based weight loss program. Unick et al. International Journal of Obesity. (2015) 10.1038/ijo.2015.89
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