The protein-sparing modified fast for obese patients with type 2 diabetes: What to expect

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Contraindications to the PSMF include a BMI less than 27 kg/m2, recent myocardial infarction, angina, significant arrhythmia, decompensated congestive heart failure, cerebrovascular insufficiency or recent stroke, end-stage renal disease, liver failure, malignancy, major psychiatric illness, pregnancy or lactation, and wasting disorders. It is also not recommended for patients under age 16 or over age 65.

In view of the risk of diabetic ketoacidosis and the difficulty of titrating required doses ofinsulin, patients with type 1 diabetes mellitus are usually not advised to undergo a low-carbohydrate or very-low-calorie diet.8,12 However, we and others have found that the PSMF can be used in some obese patients with type 1 diabetes if it is combined with appropriate education and careful monitoring.12

Major concerns about the safety of the PSMF stem from experiences with the first very-low-calorie diets in the 1970s, which were associated with fatal cardiac arrhythmias and sudden death.18 These early diets used liquid formulas with hydrolyzed collagen protein of poor biologic value and were deficient in many vitamins and minerals. Today’s very-low-calorie diets use protein sources of high biologic value (chiefly animal, soy, and egg for the PSMF) and are supplemented with necessary vitamins and minerals, reducing the risk of electrolyte and cardiac abnormalities.9,19,20 Furthermore, before starting the PSMF all patients must have an electrocardiogram to be sure they have no arrhythmias (eg, heart block, QT interval prolongation) or ischemia.

Relative contraindications

A known history of cholelithiasis is a relative contraindication to a very-low-calorie diet and may be of concern for some patients and providers. While obesity itself is already a risk factor for gallstones, gallstone formation has also been associated with bile stasis, which occurs from rapid weight loss with liquid formula diets of low fat intake (< 10 g/day).21 However, in the PSMF, fat intake from protein sources, though low (45–70 g/day), is considered high enough to allow adequate gallbladder contraction, thus decreasing the risk of gallstone formation.22

Gout is another relative contraindication, as hyperuricemia with risk of gout is also linked to high-protein diets.9 Palgi et al23 found that uric acid levels rose by a mean of 0.4 mg/dL during the diet. The risk of gout, however, seemed to be small, occurring in fewer than 1% of patients in the study. Furthermore, in a recent study by Li et al,24 uric acid levels were found to significantly decrease in patients on a high-protein, very-low-calorie diet. Nonetheless, uric acid levels should be monitored regularly in patients on the PSMF.


Common side effects of the PSMF include headache, fatigue, orthostatic hypotension, muscle cramps, cold intolerance, constipation, diarrhea, fatigue, halitosis, menstrual changes, and hair thinning. Most of these are transient and may be alleviated by adjusting fluid, salt, and supplement intake. Other side effects may disappear as the patient is weaned off the diet.8,9


Current PSMF programs are considered safe when used in combination with regular follow-up with health care providers.8,12

At Cleveland Clinic, patients meet with a dietitian twice in the first month and monthly thereafter (or more frequently if needed) for weight monitoring and education on nutrition and behavior modification (Table 1). Since the PSMF does not provide complete nutrition, daily supplementation with vitamins and minerals is required.

Daily exercise is encouraged throughout the program to increase fitness and to help keep the weight off during the refeeding phase and after.

Patients also meet every 6 to 8 weeks with the referring nurse practitioner or physician for further monitoring and evaluation of vital signs, laboratory results, and side effects. The PSMF protocol at Cleveland Clinic enables both primary care physicians and specialists (including nurse practitioners) within our network to monitor the patient’s status. Use of a common electronic medical record system is particularly valuable for easy communication between providers. If a primary care physician feels unable to appropriately counsel and supervise a patient in the PSMF program, referral to an endocrinologist or weight loss specialist is recommended.

In addition to baseline electrocardiography and monitoring of uric acid levels, a comprehensive metabolic panel is drawn at baseline, twice in the first month, and monthly thereafter to check for electrolyte imbalances and metabolic and tissue dysfunction such as dehydration, excessive protein loss, and liver or kidney injury.

Patients should not attempt the PSMF without medical supervision. Many patients have friends or family members who want to try the PSMF along with them, but this can be dangerous, especially for those with hypertension or type 2 diabetes. The medications prescribed for these conditions can result in hypotension or hypoglycemia during the PSMF.

Although there are no standard guidelines for adjusting medication use before starting a patient on the PSMF, it is logical to taper off or discontinue antihypertensive agents in patients with tightly controlled hypertension to avoid possible dehydration and hypotension during the first few diuresis-inducing weeks of the diet. In particular, diuretic agents should be discontinued to prevent further electrolyte imbalance and fluid shifts.

Similarly, in patients with tightly controlled type 2 diabetes (hemoglobin A1c < 7.0%), oral hypoglycemic agents and insulin therapy should be reduced before starting the diet to avoid potential hypoglycemia. During the course of the diet, providers should then adjust medication dosages based on follow-up vital signs and laboratory results and daily glucose monitoring.8


Though few formal studies have been done, the PSMF may have major effects on hyperglycemia, cardiovascular risk factors, and diabetic nephropathy in obese patients with type 2 diabetes, at least in the short term (Table 2).

Weight loss

In one of the first PSMF studies,23 in 668 patients with or without type 2 diabetes (baseline weight 98 kg), the mean weight loss was 21 kg after the intensive phase and 19 kg by the end of the refeeding phase.

In another observational report,25 25% to 30% of patients lost even more weight, averaging 38.6 kg of weight loss. Typically, the higher the baseline weight, the greater the weight loss during the PSMF.23

Patients with type 2 diabetes lost a similar amount of weight (8.5 kg) compared with those without diabetes (9.4 kg, P = .64) in a study of meal-replacement PSMF (using OPTIFAST shakes and bars).26 In a large meal-replacement study of 2,093 patients, Li et al24 found that weight loss was similar between diabetic, prediabetic, and nondiabetic patients. Weight loss was also closely maintained in those patients who stayed on the diet for 12 months.

In a PSMF study in which all the participants had type 2 diabetes, the mean weight loss was 18.6 kg. Although the patients regained some of this weight, at 1 year they still weighed 8.6 kg less than at baseline. However, a conventional, balanced, low-calorie diet resulted in similar amounts of weight loss after 1 year.27 Furthermore, a second round of the PSMF did not result in significant additional weight loss but rather weight maintenance.28

Fat loss and smaller waist circumference

Most of the weight lost during a PSMF is from fat tissue.11,26 Abdominal (visceral) fat may be lost first, which is desirable for patients with type 2 diabetes, since a higher degree of abdominal fat is linked to insulin resistance.2,29

After a meal-replacement PSMF, waist circumference decreased significantly in patients both with and without type 2 diabetes.24,26 However, in one study, less fat was lost per unit of change of BMI in the group with type 2 diabetes than in the nondiabetic group.26 Since insulin inhibits lipolysis, it is possible that exogenous insulin use in diabetic patients may prevent greater reductions in fat mass, though this is likely not the only mechanism.26

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