Caloric restriction

Caloric restriction or calorie restriction, also known as energy restriction or a hypocaloric diet, is a type of dietary regimen that reduces caloric intake without incurring malnutrition and getting all essential nutrients.

Uses
The main use of calorie restriction diets is for weight loss.

Clinically caloric restriction is often used to reduce obesity levels, and to treat or manage illnesses that are associated with increased rates of obesity, for example cardiovascular disease, type 2 diabetes and metabolic syndrome. Clinical trials have also been carried out on critically ill patients, especially where obesity is a risk factor for the illness, and in people requiring enteral or parental feeding (tube feeding).

Theory
There is some evidence that caloric restriction reduces the impaired immune function caused by aging, reduces the risk of age-related illnesses, and extends lifespan. Calorie restriction or other dietary changes and exercise are the main approaches recommended for weight loss in healthy people.

ME/CFS
Caloric restriction has not been suggested as a core treatment or cure for ME/CFS, since it is not a nutritional or lifestyle related disease, however it may help some patients with certain comorbidities or reduce some ME/CFS symptoms.

Obesity is common in Americans with ME/CFS and the exercise intolerance experienced by ME/CFS patients means that dietary change is likely to the main aporoach for those wishing to lose weight. Fibromyalgia patients may experience a reduction in pain and other symptoms.

Many people with ME/CFS are of normal weight, and some patients with very severe ME have severe gastrointestinal dysfunction causing severe weight loss and malnutrition, this means caloric restriction will not be safe for all patients.

Small studies have shown that hypocaloric diets can reduce inflammation in people without ME/CFS, which may improve some ME/CFS symptoms since raised inflammation markers and neuroinflammation are caused by ME/CFS. Reducing inflammation may reduce pain. Hypocaloric diets are flexible enough to combine with other forms of dietary plan in order to maximise possible benefits.

Evidence
Evidence is very weak due to a lack of trials. It is not generally recommended by clinicians specializing in ME/CFS.

Risks and side effects
Risks in people with ME/CFS are unclear due to a lack of clinical trials.

Navarro et al. report that hypocaloric diets that restrict calorie intake too severely, for example to 1,000kcal or less per day, are dangerous rather than beneficial. Rapid weight loss caused by inadequate food take in a known cause of fatigue and can cause harmful metabolic changes, including rapid reduction in muscle.

People with ME/CFS are known to have nutritional deficiencies caused by the disease rather than by diet, so it is not clear how a long-term hypocaloric diet may need to be adapted to avoid malnutrition.

Costs and availability
Inexpensive and no particular foods are needed, although it will generally be more expensive than low quality highly processed foods.

ME/CFS commonly causes significant disability, this may mean any dietary change involving additional cooking or meal planning may worsen symptoms, however this is true of almost all dietary changes, and a hypocaloric diet does not exclude pre-prepared foods.

Notable studies

 * 2011, A legume-based hypocaloric diet reduces proinflammatory status and improves metabolic features in overweight/obese subjects (Full text)
 * 2014, Hypocaloric vs Normocaloric Nutrition in Critically Ill Patients: A Prospective Randomized Pilot Trial (Full text)
 * 2015, Mitoprotective dietary approaches for myalgic encephalomyelitis/chronic fatigue syndrome: caloric restriction, fasting, and ketogenic diets (Abstract)
 * 2015, The effects of gluten-free diet versus hypocaloric diet among patients with fibromyalgia experiencing gluten sensitivity symptoms: protocol for a pilot, open-label, randomized clinical trial (Full text)
 * 2020, Impact of a Moderately Hypocaloric Mediterranean Diet on the Gut Microbiota Composition of Italian Obese Patients (Full text)