Losing weight fast: possible, but at what cost?

01The short answer

02What you lose in the first days

A scale that drops in the first week is not measuring fat lost. Nova Scotia's 811 health page puts it simply: with a fad diet, much of the weight you lose is likely water and muscle, not body fat, and the weight can come back after the diet. A review published in 2001 in the Cleveland Clinic Journal of Medicine reached the same conclusion for low-carbohydrate diets: the initial “fast” loss is water.

Losing muscle is not a detail. Muscle helps you move, carry and stay strong over the years; the Canadian guidelines call for muscle strengthening at least twice a week for every adult.

03Why experts advise going slower

The NIDDK notes that losing weight very quickly may raise your chances of forming gallstones. It explains that experts recommend beginning with a loss of 5 to 10% of your starting weight over 6 months, and advises losing weight at a slower pace and keeping it off over time.

Very low-calorie diets, around 800 calories a day or less, are defined by the NIDDK as diets supervised by a health care professional. This is not a plan to follow on your own: before starting one, the NIDDK advises talking with your doctor, including about the risk of gallstones.

04“10 pounds in 2 weeks”: the promises to avoid

The NIDDK advises staying away from programs that promise, for example, to lose 30 pounds in 30 days, or to lose weight without diet or exercise. Nova Scotia's 811 page warns against diets that promise more than 1 or 2 pounds a week. The Competition Bureau of Canada adds two warnings: be wary of weight loss presented as permanent even after you stop the product, and don't trust “before” and “after” photos.

For products, Health Canada is clear: there is no magic pill that makes you lose weight effortlessly, and if a product sounds too good to be true, it probably is. Before buying a health product, check that it carries an eight-digit Health Canada number (DIN or NPN) on the package.

05“Burn fat while you sleep”: sleep still matters

No night replaces an active week, but sleep is part of the guidelines. The Canadian 24-Hour Movement Guidelines ask adults aged 18 to 64 for 7 to 9 hours of good-quality sleep, with consistent bed and wake-up times. In the U.S., the National Heart, Lung, and Blood Institute (NHLBI) notes that sleep deficiency is associated with several health problems, including obesity, and that adults who regularly sleep 7 to 8 hours have a lower risk of obesity. That is an association, not a recipe; but sleeping enough is part of the same guidelines as moving.

06Making progress, without shortcuts

What really moves things forward is less spectacular than an extreme diet. The American College of Sports Medicine associates more than 250 minutes of activity a week with clinically significant weight loss. Obesity Canada notes that health behaviour changes usually bring 3 to 5% weight loss, which can already meaningfully improve obesity-related health problems. In other words: more minutes in the week, and habits that last.

That is where a fixed-time class helps. Joanie Roussy's women's classes, at noon on weekdays, offer Strong Nation™, Bootcamp and Zumba®, with no experience needed; Joanie, a certified NOOM coach, also offers private, personalized 60-minute training sessions on request, based on each woman's needs and goals. Adult karate, which is mixed, is also open to everyone from 14. Losing weight: what actually works says more about habits.

07From Le Sud-Ouest, a little every day

A few extreme days count for less than being active every day. In Le Sud-Ouest, the Lachine Canal path lends itself to walking or cycling on days without class; from Griffintown or Pointe-Saint-Charles, getting to the dojo maps the way to 550 chemin du Golf, suite 010, on Nuns' Island. The women's classes are at noon, adult karate in the evening: the schedule gives the days.

Sources

1. Nova Scotia 811, “Nutrition for Weight Loss: What You Need to Know About Fad Diets” (2025) — 811.novascotia.ca/health_topics/nutrition-for-weight-loss-what-you-need-to-know-about-fad-diets/
2. Blackburn et al., Cleveland Clinic Journal of Medicine (2001) — www.ccjm.org/content/68/9/761.full.pdf
3. NIDDK, “Dieting & Gallstones” — niddk.nih.gov/health-information/digestive-diseases/gallstones/dieting
4. NIDDK, definition of a very low-calorie diet — www.niddk.nih.gov/Dictionary/V/very-low-calorie-diet
5. NIDDK, “Choosing a Safe & Successful Weight-loss Program” — niddk.nih.gov/health-information/weight-management/choosing-a-safe-successful-weight-loss-program
6. CDC, “Losing Weight” (2025) — www.cdc.gov/healthy-weight-growth/losing-weight/index.html
7. Competition Bureau Canada, warning of January 15, 2018 — www.canada.ca/en/competition-bureau/news/2018/01/experiencing_thepost-holidayweightbluesbecarefulmanydietsorfat-b.html
8. Health Canada, safe use of health products for weight loss (2012) — www.canada.ca/en/health-canada/services/drugs-medical-devices/safe-use-health-products-weight-loss.html
9. CSEP, Canadian 24-Hour Movement Guidelines, adults 18–64 (2020) — csepguidelines.ca/guidelines/adults-18-64/
10. NHLBI, “Sleep Science and Sleep Disorders” — www.nhlbi.nih.gov/science/sleep-science-and-sleep-disorders
11. Donnelly et al., American College of Sports Medicine position stand, Med Sci Sports Exerc (2009) — doi.org/10.1249/MSS.0b013e3181949333
12. Obesity Canada, adult obesity guideline, CMAJ (2020) — www.cmaj.ca/content/cmaj/192/31/E875.full.pdf

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