Health benefits of weight loss

This page has been written by Dr Priya Sumithran and reviewed by A/Prof Samantha Hocking

Type 2 diabetes

Weight loss of 5% in insulin resistant adults with obesity improves insulin sensitivity in fat, liver and muscle, and insulin production from the pancreas,¹ and these parameters improve progressively with additional weight loss. This has clinical implications for the prevention and treatment of type 2 diabetes (T2D).

Several large studies have shown that in people with pre-diabetes, weight loss of 5–7% induced by changes in diet and physical activity can reduce progression to T2D by nearly 60% over 3 to 4 years.²³ Every kilogram of weight lost was associated with an estimated 16% reduction in risk of development of T2D.⁴

The benefits of modest weight loss extend also to people with established T2D. In a study of >5000 people with T2D, improvements in glycaemic control were seen with as little as 2–5% weight loss,⁵ while greater weight loss brought about progressive benefits in fasting glucose and HbA1c (a measure of average blood glucose).⁶ Similarly, in adults with overweight or obesity with a recent (<6 years) diagnosis of T2D, an intensive lifestyle intervention program comprising a low-energy formula diet for 3–5 months followed by stepped food reintroduction and structured support over 12 months resulted in diabetes remission at 12 months in nearly half (46%) of participants in the intervention group, compared with 4% of participants in the control group (average weight loss 10kg vs 1kg). Remission of T2D was related to the amount of weight lost, occurring in none of the participants who gained weight, and 7%, 34%, 57% and 86% of participants who lost 0–5kg, 5–10kg, 10–15kg, and more than 15kg, respectively.⁷ The durability of diabetes remission was linked to the extent of sustained weight loss.⁸

Bariatric surgery is recommended in national and international guidelines for treatment of T2D.⁹¹⁰ A randomised study in which 150 people with obesity and T2D were treated with intensive medical therapy with or without bariatric surgery (Roux-en-Y gastric bypass [RYGB] or sleeve gastrectomy [SG]) showed that 5 years after randomisation, both types of surgery were superior to intensive medical therapy alone in achieving excellent glycaemic control and reducing the use of glucose-, lipid- and blood pressure-lowering medications.¹⁰ The beneficial effects of RYGB and SG on glycaemic control appear to be related not only to weight loss but to additional metabolic effects.¹¹

Fatty liver disease

Improvements in fatty liver are also seen with relatively small weight losses. Imaging studies have shown that weight loss of 5% over 12 months reduces liver fat content by 33% in people with T2D, with stepwise further reductions with greater weight loss (up to 80% reduction in liver fat with >10% weight loss).¹² Loss of ≥7% initial weight is associated with significant improvements in liver inflammation and injury on liver biopsy.¹³

Cardiovascular risk factors and events

A meta-analysis of 83 weight loss intervention studies found that any weight loss significantly reduced blood pressure and triglycerides over 2 years.¹⁴ A graded improvement with progressive weight loss is seen in these parameters, starting with as little as 2–5% weight loss (for systolic blood pressure and triglycerides) and 5–10% weight loss (diastolic blood pressure and high-density lipoprotein cholesterol).⁶

Although an improvement in cardiovascular risk factors is consistently shown, it is not clear whether small amounts of weight loss are sufficient to improve cardiovascular outcomes. A randomised trial of >5000 adults with T2D aged 45–76 years who were overweight or had obesity showed no difference in the occurrence of cardiovascular events over 10 years’ follow-up between people randomly assigned to an intensive lifestyle-based weight loss intervention compared with diabetes support and education.¹⁵ However, a subsequent analysis of the data suggests an association between magnitude of weight loss and cardiovascular events, as people who lost ≥10% of their body weight in the first year of the study had a 21% lower risk of cardiovascular events and mortality compared with individuals with stable weight or weight gain.¹⁶ A meta-analysis of lifestyle interventions in adults with obesity did not find a significant effect of weight loss on the development of new cardiovascular events or on cardiovascular mortality, but did demonstrate a reduction in all-cause mortality (34 trials, 685 events; risk ratio 0.82, 95% confidence interval 0.71 to 0.95) for weight loss, equating to six fewer deaths per 1000 participants.¹⁷ Another meta-analysis in patients with established coronary artery disease reported a 37% reduction in a composite outcome of all-cause mortality, cardiovascular mortality, and major adverse cardiac events with intentional weight loss.¹⁸

Although individual studies have not shown a mortality benefit with modest weight loss, a meta-analysis of randomised controlled trials involving >17,000 adults with obesity reported a 15% reduction in all-cause mortality with intentional weight loss of 5.5kg.¹⁹ Cohort studies have shown a mortality benefit with greater weight loss after bariatric surgery. For example, Swedish Obese Subjects study, in which bariatric surgery produced an average of 16–18% weight loss, found a 29% reduction in overall mortality after 10–20 years, compared with a matched unoperated control group which did not lose weight.²⁰

Obstructive sleep apnoea

Clinical trials indicate that moderate weight loss of >10kg in people with obesity is beneficial in the treatment of obstructive sleep apnoea (OSA), with improvements in nocturnal respiratory disturbances (apnoea-hypopnoea index) and symptoms (Epworth Sleepiness Score) related to the degree of weight loss.²¹²²²³

Osteoarthritis

In older adults with knee osteoarthritis, a combination of diet and exercise intervention resulting in weight loss of 5.7% produced better overall improvements in self-reported and objectively measured physical function, as well as knee pain, compared to a control group (weight loss 1.2%). Functional benefits were limited in participants who received either the diet or exercise intervention alone.²⁴

Cancer

A meta-analysis of randomised controlled trials of various non-surgical weight loss interventions in people with obesity did not find a significant reduction in cancer incidence or mortality after modest weight loss (overall mean 3.4kg at 1 year).¹⁷ Greater weight losses may be beneficial: larger cohort studies in people with obesity have reported a decreased incidence of all cancers and obesity-related cancers in women who intentionally lost at least 9kg in adulthood,^{25 26} but not men,²⁷ and meta-analyses of controlled cohort and population-based studies have demonstrated a 28–58% reduction in overall incidence of cancer, as well as specific reductions in the incidence of obesity-related cancer and breast cancer following bariatric surgery.²⁸²⁹

Reproductive and genito-urinary issues

In women with polycystic ovary syndrome (PCOS), lifestyle intervention reduces clinical and biochemical hyperandrogenism (excess male hormone levels), even if minimal weight loss (mean 1.7kg over 15 studies) is achieved.³⁰ Greater weight loss after bariatric surgery has been shown to bring about a six-fold reduction in the incidence of PCOS, as well as attenuation of symptoms including menstrual irregularity and excess hair growth.³¹ In sub-fertile women with overweight and obesity, 4kg weight loss resulting from diet and exercise interventions improved ovulation and increased the odds of natural pregnancy, with no difference seen in assisted reproductive outcomes.³² Weight loss of 5–10% in men and women with obesity has been shown to improve urinary stress incontinence and sexual dysfunction.^{333435 36}

Mental health and quality of life

Weight loss intervention studies have generally reported a reduction in symptoms and prevalence of depression after treatment of obesity,³⁷³⁸ although after bariatric surgery, particularly Roux-en-Y gastric bypass, a subgroup of patients exhibit an increased risk of depression and suicide, the cause for which has not been clearly identified. All treatments for obesity, particularly bariatric surgery, are consistently shown to be associated with an improvement in physical domains of health-related quality of life, but outcomes have been mixed for psychological aspects quality of life.³⁹

Lifestyle intervention without weight loss

For most people, it is difficult to achieve sustained weight loss. Fortunately, lifestyle changes can lead to improvements in many of the complications of excess weight, even if minimal weight loss occurs. For example, exercise training without caloric restriction leads to improvements in endothelial function,⁴⁰ visceral adiposity,⁴¹ liver fat⁴² and quality of life.⁴³ In people with pre-diabetes undertaking a lifestyle intervention, although weight loss was the dominant predictor of reduced diabetes incidence, the risk of development of T2D was reduced by 44–70% in people who achieved the physical activity goal of 2.5 to 4 hours per week of moderate intensity activity, even if they did not achieve the target 5–7% weight loss.³⁴