1000 Calorie Diets Aren’t as Great as You Might Think

Calorie deficit, eating and drinking fewer calories than what the body burns, is a proven method of losing weight ( 1 ).

Many diets have been designed to achieve calorie deficits, with some of them referred to as extreme diets. Such diets attain extreme calorie deficits by reducing calorie intake to only 1000 calories a day ( 2 ).

Extreme diets include low-carbohydrate/high-fat, low-fat/high-carbohydrate, and very low calorie diets, among others.

Two researchers evaluated the pros and cons of popular extreme diets by analyzing and discussing the methods and conclusions of previously published studies ( 3 ). Their findings shed more light on the effectiveness of extreme diets in long-term weight loss.

Review of published studies on popular extreme diets

Low carbohydrate/high-fat diets

This diet gives greater importance to carbohydrate restriction than fat. Some advantages of the low carbohydrate/high-fat diet include decreased glucose and insulin levels and appetite suppression. These benefits have been confirmed by the Prospective Urban and Rural Epidemiological Study (PURE) study ( 4 ).

The PURE study involving 135,335 participants showed that high carbohydrate intake improved non-cardiovascular health. However, the PURE study didn’t support the extreme reduction of fat or consuming excessive amounts of carbohydrates.

Several studies have reported the side effects of low carbohydrate/high-fat diets, which include bone loss, increased blood uric acid concentrations, increased risk of cancers, and increased mortality ( 4 , 5 ).

Low-fat/high-carbohydrate diets

This diet contains about 11-19 percent fat and a high proportion of carbohydrates. The aim is to consume more complex carbohydrates and vegetables, egg white, whole grains, and beans, and non-fat dairy are usually part of this diet.

Metabolic benefits of this diet include a reduction in total cholesterol, especially low-density lipoprotein, which has been linked with a higher risk of cardiovascular disease. In addition, blood pressure, insulin levels, and blood glucose may be reduced, which is beneficial for hypertensive and diabetic patients ( 6 , 7 ).

The major problem with low-fat diets is palatability. Some amount of fat is needed for diets to be palatable, and by reducing fats by extreme amounts, it becomes challenging to comply with low-fat/high-carbohydrate diets.

Very low calorie diets (VLCDs)

VLCDs provide rapid, short-term weight loss by providing less than 800 calories per day. Essential vitamins, minerals, and sufficient protein are taken to preserve lean body mass, which is the difference between total body weight and body fat weight. This is important for preventing weak bones, boosting immunity, and avoiding calorie imbalances. VLCDs may also help reverse type-2 diabetes as the blood glucose levels of diabetics were significantly reduced for several months ( 8 ).

Known side effects of VLCDs include cholelithiasis, ketosis, and increased serum uric acid concentrations. More research must be done on these diets to evaluate their safety profile. In addition, it’s still unknown whether VLCDs can cause any micronutrient deficiency.


Despite the apparent benefits of extreme diets, they don’t work in the long run. The main reason behind this isn’t even the side effects of the diets though 1000-calorie-a-day diets aren’t safe long-term. It’s the sheer boredom associated with them. Also, most people can’t sustain eating only 1000 calories a day. The human body needs more than that, as the average female adult needs about 1,800–2,400 calories daily, while the average male adult needs about 2,400–3,200 calories ( 1 ).

Long-term compliance is a big issue with extreme diets, and many people will eventually return to their regular diets and regain whatever weight they’ve lost. As a result, many extreme diets have experienced tremendous popularity, only to fall just as quickly as they rose.

Two things are essential for any weight-loss program – achieving weight loss and maintaining weight loss. Extreme diets have shown not to support the latter; thus, other types of diets should be utilized. It’s worth mentioning there is no one-fit-all diet. Weight loss diets should be individualized to improve the chances of success.

Alternative to Extreme Diets

Since extreme weight isn’t sustainable for long, a different approach can be used for achieving long-term weight loss. This approach is the balanced weight loss diet which contains equal quantities of fat and carbohydrates (about 30 to 40%) while the rest of the diet should be protein.

The diet should be planned to achieve a deficit of 500 to 1000 calories per day. Since a wide range of food choices is allowed, complying with a balanced weight loss diet should be convenient.

Studies have revealed that individuals on balanced weight-loss diets can build healthy eating habits. In addition, their LDL cholesterol and triglyceride levels improved, resulting in better physical fitness ( 8 ).

Scientific evidence continues to show that physical activity can help to lose weight ( 9 ). This means enough exercise should accompany any dietary therapy. In addition, since compliance with weight loss treatments is affected by motivation, proper counseling by dieticians or counselors is vital to ensure compliance. Obesity and overweight should be tackled with a slow and steady method that’s sustainable in the long run and not ‘crash diets’ as they often fail long term.


1. WebMD (2023) Calorie Deficit: What to Know.

2. Fetters K. (2021) What Happens to Your Body When You Go on an Extreme Diet?

3. Joshi S, Mohan V. Pros & cons of some popular extreme weight-loss diets. Indian J Med Res. 2018 Nov;148(5):642-647. doi: 10.4103/ijmr.IJMR_1793_18. PMID: 30666989; PMCID: PMC6366252.

4. Dehghan M, Mente A, Zhang X, Swaminathan S, Li W, Mohan V, et al. Associations of fats and carbohydrate intake with cardiovascular disease and mortality in 18 countries from five continents (PURE): a prospective cohort study. Lancet. 2017 Nov 4;390(10107):2050-2062. doi: 10.1016/S0140-6736(17)32252-3. Epub 2017 Aug 29. PMID: 28864332.

5. Joshi S. Obesity diets-fact or fiction. Med Update 2007; 17 : 913-7.

6. Gardner CD, Kiazand A, Alhassan S, Kim S, Stafford RS, Balise RR, Kraemer HC, King AC. Comparison of the Atkins, Zone, Ornish, and LEARN diets for change in weight and related risk factors among overweight premenopausal women: the A TO Z Weight Loss Study: a randomized trial. JAMA. 2007 Mar 7;297(9):969-77. doi: 10.1001/jama.297.9.969. Erratum in: JAMA. 2007 Jul 11;298(2):178. PMID: 17341711.

7. Anderson JW, Chen WJ, Sieling B. Hypolipidemic effects of high-carbohydrate, high-fiber diets. Metabolism. 1980 Jun;29(6):551-8. doi: 10.1016/0026-0495(80)90081-5. PMID: 6247602.

8. Steven S, Hollingsworth KG, Al-Mrabeh A, Avery L, Aribisala B, Caslake M, Taylor R. Very Low-Calorie Diet and 6 Months of Weight Stability in Type 2 Diabetes: Pathophysiological Changes in Responders and Nonresponders. Diabetes Care. 2016 May;39(5):808-15. doi: 10.2337/dc15-1942. Epub 2016 Mar 21. Erratum in: Diabetes Care. 2018 Apr 24;: PMID: 27002059.

9. Health Line. The Importance of Weight Loss and Exercise.