Diet or exercise: Which works best for weight loss?

The Bottom Line

  • Improving your diet is more effective than exercising to lose weight, but a combination of diet changes AND exercise has the greatest benefits for weight loss and heart health.
  • Start small: Nutrition expert Dr. Russell De Souza suggests one small diet change and 5 minutes of exercise each day can help build long term healthy habits to keep the pounds off.
  • Measuring your waist circumference is a more accurate indicator of weight loss impacts on heart health than measuring your weight on the scale.

We’ve all seen ads for “miracle” diets, pills or other weight loss plans. We may even have tried one or two only to discover they’re fads that don’t live up to their claims. As many studies have shown – and you may have heard before – the basis of most successful weight loss is eating less and exercising more.

But just out of curiosity, which is more important? We often joke about needing to take an extra walk around the block to validate that extra slice of cake or serving of Thanksgiving turkey. Does exercise really help counter those extra calories, or do diet changes make a bigger difference?

That’s what a recent systematic review hoped to discover (1). It included 21 randomized controlled trials involving more than 3,500 overweight adults aged 35 to 70 who took part in diet and/or exercise programs lasting between 1-6 years. The diets emphasized low-fat, high fibre foods including fruits and vegetables, while the exercise programs included both aerobic activity (e.g. walking) and resistance training done on a regular basis.

“Before and after” body measurements (weight, body fat and waist circumference) and cardiovascular health readings (fitness level, blood pressure and cholesterol) of all the participants were taken to help determine the most effective way to drop weight, reduce body fat and improve heart health.

What the research tells us

The verdict? Sorry, those extra steps are likely not enough to burn off extra calories. Like previous studies (2,3) the review confirms that changes in diet contribute more to weight loss than exercise.

However, the review emphasizes that the best results come from a combination of both. As McMaster University’s Dr. Russell de Souza says, that’s the important message people should take to heart – literally!

The overwhelming prevalence of obesity means that more and more people are at high risk for cardiovascular problems (4,5). Dr. de Souza, registered dietitian and nutrition epidemiologist with McMaster University’s Department of Clinical Epidemiology & Biostatistics, explains that diet and exercise actually work hand in hand to reduce the risk of heart disease by lowering body weight and fat as well as blood pressure – which is known as the “silent killer” because it is a significant factor in heart attacks and kidney disease (6,7).

When it comes to weight loss, Dr. de Souza says the challenge is to go about it in a sensible, healthy way so that it’s sustainable.

“When people go to extremes with exercise or diet it can result in injuries or rebound food cravings. I recommend people start off slow by going for the ‘low hanging fruit’ such as actually having a piece of fruit or a salad and walking for five minutes every day. Once that becomes a habit it is easier to incorporate other healthy actions.” The good news, he adds, is that once you start, your body responds very quickly to exercise so that before long five minutes becomes 30 minutes – or more – each day.

You can ensure you are on the right track by monitoring your weight or BMI (body mass index) but Dr. de Souza suggests one of the best and simplest measures is waist circumference: men should aim to stay below 102 cm and women no more than 88 cm. Aiming even lower than these conservative estimates may be even better: a recent systematic review found that heart health risks increase for women with waist measurements over 75 cm (8). “The higher the number,” explains Dr. de Souza, “the more visceral fat being stored around your internal organs and in your liver.”

Dr. de Souza believes successful weight loss takes patience and persistence. “It’s a long-term effort. It took some time to put on those pounds and it’s going to take some time to take them off in a way that’s healthy and will keep them off!”

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  1. Schwingshackl L, Dias S, Hoffman G. Impact of long-term lifestyle programmes on weight loss and cardiovascular risk factors in overweight/obese participants: A systematic review and network meta-analysis. Syst Rev. 2014; 3:130.
  2. Shaw KA, Gennat HC, O’Rourke P et al. Exercise for overweight or obesity. Cochrane Database Syst Rev. 2006; Issue 4. Art. No.: CD003817. DOI: 10.1002/14651858.CD003817.pub3.
  3. Curioni CC, Lourenco PM. Long-term weight loss after diet and exercise: A systematic review. Int J Obesity. 2005; 29(10):1168–1174.
  4. World Health Organization (WHO). Obesity and overweight. 2019. 
  5. Guh DP, Zhang W, Bansback N et al. The incidence of co-morbidities related to obesity and overweight: A systematic review and meta-analysis. BMC Public Health. 2009; 9:88.
  6. Yusuf S, Hawken S, Ôunpuu S, Dans T, Avezum A, Lanas F, McQueen M, Budaj A, Pais P, Varigos J, Lisheng L. Effect of potentially modifiable risk factors associated with myocardial infarction in 52 countries (the INTERHEART study): case–control study. Lancet 2004; 364:937-952
  7. Centers for Disease Control and Prevention. High blood pressure. 2016.  
  8. Aune D, Sen A, Norat T et al. Body mass index, abdominal fatness, and heart failure incidence and mortality: A systematic review and dose-response meta-analysis of prospective studies. Circulation. 2016; 133(7):639-649.

DISCLAIMER: These summaries are provided for informational purposes only. They are not a substitute for advice from your own health care professional. The summaries may be reproduced for not-for-profit educational purposes only. Any other uses must be approved by the McMaster Optimal Aging Portal (

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