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Clinically Proven

Optifast products are backed by strong clinical evidence that shows they can help people achieve sustainable weight loss. Our scientists are continually updating Optifast products and programmes to reflect the latest weight loss science.

Here is just a sample from all publications available on Optifast:


The Optifast OPTIWIN1 study is one of the largest RCTs of meal replacement programmes ever conducted. The OPTIWIN study was conducted by Professors Jamy D. Ard, MD and Kristina H. Lewis, MD, MPH from the Wake Forest School of Medicine and was published in Obesity, the official journal of the Obesity Society. OPTIWIN compares a weight loss programme using Optifast with a widely recommended food-based diet.

The programme using Optifast was proven more effective with greater sustained weight loss thanthe food-based diet. Patients lost approximately twice as much weight using the Optifast programme and kept it off. Optifast patients also lost more fat mass.

Intermittent fasting study

A review of available clinical trials published in The New England Journal of Medicine 3 has suggested that intermittent fasting has benefits for many health conditions, such as obesity, diabetes,cardiovascular disease, cancers, and neurologic disorders.

Optifast was evaluated in an intermittent fasting study entitled, “Alternate day fasting combined with a low carbohydrate diet for weight loss, weight maintenance, and metabolic disease risk reduction” 4 by Professor Krista A. Varady, PhD, from the University of Illinois. The study was published in Obesity Science and Practice. Optifast shakes were used as low-carbohydrate meal replacements.

The study suggests that alternate day fasting combined with a low carbohydrate diet or Total Diet replacement like Optifast may likely be effective for weight loss, weight maintenance, and improvement of certain metabolic disease risk factors such as high cholesterol, blood pressure, and insulin levels.

Craving control study

One theory behind a Total Diet Replacement is that it works in part by limiting the amount of time a person thinks about food. With a programme using Optifast, there is no food shopping, meal planning or cooking. For this reason, a total diet replacement may have a positive impact on food cravings'.

To test this theory, Optifast was evaluated in a study entitled, “Effects of 3-week total meal replacement vs. typical food-based diet on human brain functional magnetic resonance imaging food-cue reactivity and functional connectivity in people with obesity,” 5 In other words, scientists looked at the part of the brain responsible for cravings to see if the two diets produced different effects when looked at on a Magnetic Resonance Imaging (MRI) machine.

The scientists found differences in the ways the diets “lit up” the brain on the MRI machine. But more importantly, the study found that patients using Optifast lost significantly more weight and had reduced food cravings compared with the people on the food-based diet. While further research is needed, this study suggests that using Optifast as a total diet replacement may help control the urge to eat. The study was conducted by Professor Chanaka N. Kahathuduwa MD, PhD of Texas Tech University and published in the medical journal Appetite 5

Diabetes Remission study

In one large U.K. study, almost half of the participants on a Total Diet Replacement programme achieved remission to a non-diabetic state and were able to stop taking their diabetes medication.6

In addition, multiple studies2, 7,8,9,10 of Optifast programmes across the globe (Australia, Canada, Germany & USA) have demonstrated the ability to reduce the incidence of diabetes, improve blood sugar levels and limit the need for diabetes medications. For example, a study using Optifast shakes, “Very Low-Calorie Diet and 6 Months of Weight Stability in Type 2 Diabetes: Pathophysiological Changes in Responders and Non responders,”10 also found that losing weight with a TDR plan can help put Type 2 Diabetes into remission. The study was conducted by Professor Sarah Steven of Newcastle University and published in Diabetes Care.

In this study of Type 2 Diabetics using Optifast products to lose weight, 40% of the study participants were able to put their Type 2 Diabetes into remission for at least six months without using medication. Participants in this study experienced an average weight loss of 14.2 kg.

1. Ard JD, Lewis KH, Rothberg A, et al. Effectiveness of a total meal replacement program (Optifast program) on weight loss: results from the OPTIWIN study. Obesity. 2018; doi: 10.1002/oby.22303.
2. Bischoff SC, et al. Multicenter evaluation of an interdisciplinary 52-week weight loss
program for obesity with regard to body weight, comorbidities, and quality of life: a prospective study. Int JObesity. 2012;36(4):614-624
3. de Cabo R, and Mattson MP, Effects of Intermittent Fasting on Health, Aging, and Disease. N Engl J Med2019; 381:2541-2551DOI: 10.1056/NEJMra1905136
4. Varady K et al. Alternate day fasting combined with a low‐carbohydrate diet
for weight loss, weight maintenance, and metabolic disease risk reduction. Obesity Science and Practice 2019;DOI: 10.1002/osp4.367 5. Kahathuduwa CN, et al. Effects of 3-week total meal replacement vs. typical food-based diet on human brain functional magnetic resonance imaging food-cue reactivity and functional connectivity in people with obesity. Appetite. 2018.
6. Lean MEJ, et al. Primary Care-Led Weight Management for Remission of Type 2 Diabetes (DiRECT): An Open-label, Cluster-Randomised Trial. Lancet. 2017: Published online Dec 5, 2017
7. Shiau JY, et al. Effects on diabetes medications, weight and A1C among patients with obesity and diabetes: 6-month observations from a full meal replacement, low-calorie diet weight management program. an JDiabetes. 2017 ;Jun 6. pii: S1499-2671(17)30045-X.
8. Ard J, et al. Practical application of a comprehensive weight management program in patients with and without metabolic syndrome. J Obes Wt Loss Ther. 2014;S4:007.
9. Gow Ml, et al.Reversal of type 2 diabetes in youth who adhere to a very-low energy diet: a pilot study. Diabetologia. 2017;60:406-415.
10. Steven S, et al.Very-low-calorie diet and 6 months of weight stability in type 2 diabetes: pathophysiologic changes in responders and non responders. Diabetes Care. 2016;39(5):808-815.
11. NICE Guidelines 2008 [amended 2014] point 1.2.5. Available at https://www.nice.org.uk/guidance/cg177/chapter/1-Recommendations#education-and-self-management-2