Sonja Bakker (Avenhorn, November 3, 1974) is a Dutch weight consultant and writer. She briefly had a large audience.
Bakker grew up in an entrepreneurial family, her father has a flower bulb company in Avenhorn. She graduated from domestic science school in 1990 and completed the meao (economic and administrative direction) in 1993. After the meao, Bakker worked as a P&O employee at Christine le Duc BV in Volendam. She had tried several diets herself before starting the LOI written weight consultant course in 1995, which she graduated in 1997. She then followed a course in orthomolecular nutrition, on the basis of which she developed her own diet method to lose weight. In 1997 she started her own weight consultant practice.
Bakker is the author of the book Reach your ideal weight !, of which 400,000 copies were sold in 2005 and 2006. The book has strict weekly menus, which should be the key to weight reduction. Reach your ideal weight! was continuously in the top 10 of the most sold books in the Netherlands from the second week of 2006 to March 2007. A later book, Reach and maintain your ideal weight, was regularly the best-selling book in the fifteen weeks to mid-March 2007.
After the success of her first book, Bakker set up an online weight loss program. This method for weight loss was included in the supplementary insurance package by the Dutch health insurer Univé.
After she had been a guest in various television programs, Bakker was part of the fifth season of the television program Jealous Age in October 2006. The commercial channel SBS6 hired Bakker as a potential audience rating gun, with the intention of giving the program a new impulse. In Your Real Age she guided candidates on their way to a healthy weight.
Bakker has written columns for Noordhollands Dagblad, Haarlems Dagblad, IJmuider Courant, Leidsch Dagblad and De Gooi- en Eemlander. She was the editor-in-chief of the magazine Flair once. From January 2007 a monthly column by her hand appeared in the magazine Santé. Her first book Reach Your Ideal Weight! in 2007 under the title Erreichen Sie Ihr Traumweight! released on the German market. For this, Bakker conducted extensive research in German supermarkets, where she looked at what products were sold that would not look out of place in her method.
Bakker also gave lectures for doctors, hospital staff and the business community. During these lectures she emphasizes the importance of a healthy diet. She also addressed the problem of lack of motivation in people who want to lose weight. According to her, this could be tackled by having weight-lossers mainly snack in between meals, to prevent the bigger tempters, such as fatty snacks, from being resisted.
In 2009 Sonja Bakker divorced her husband, with whom she has two sons. This is the publisher of her books. Bakker had a third son in a subsequent relationship in 2012.
Bakker is not a dietician and is criticized by many dieticians. Despite this, her method is very popular and many dieters use the term sonja bakers, for dieting according to her method. Maintaining weight with this diet is a matter of following a diet six days a week and one day a SAS day (Schijt-Aan-Sonja), as the supporters call it.
The Netherlands Nutrition Center criticized Bakker’s diet.  It confirmed that following Bakker’s method leads to weight loss, but according to the Nutrition Center, the method offers insufficient tools to develop a healthy eating pattern in the long term, so that the dropout can actually stay slim. The tips in her books are fairly brief and are limited to “three main meals a day” and “enough exercise”. The Netherlands Nutrition Center doubted whether this limited information is sufficient to structurally adjust the diet and thus reduce the risk of relapse.
The Nutrition Center further pointed out that the books contain “facts” that do not agree with scientific research. Examples of this were that coffee would remove moisture from the body, that white wine would cause cellulite and that fruit would cleanse the body. The Nutrition Center also found that bread and dairy play a subordinate role in Bakker’s menus, which is not in accordance with the Wheel of Five.
The dietitian profession is also critical of the recommendations of what they call “diet gurus” such as Sonja Bakker. From that angle, there are warnings about the health risks of all kinds of fashionable diets and also about an overly rosy presentation of the results.
The Nijmegen psychologist Tatjana van Strien criticized Bakker’s diet. In her book on weight loss with and without results, Van Strien called it a “crash diet”, which can result in permanent problems with metabolism and eating behavior. According to Van Strien, Bakker’s diet causes a self-imposed famine, because the body switches to “emergency ration” and is therefore extra frugal with the energy supplied. 
Allegation of plagiarism
On September 19, 2006, Bakker was accused of plagiarism by her colleague Bea Pols, weight consultant in Heerhugowaard. In her book Reach Your Ideal Weight! Bakker is said to have copied exactly twenty sentences from the book Slimming and personal growth written by Pols in 2003. Pols followed the same LOI course as Bakker. Bakker has contradicted these allegations and said he suspected that Pols used attachments that Bakker had provided to her clients in the past.   Later, Pols also accused Bakker of plagiarizing passages from various other books. Pols wrote the book “Without a fight, no truth” about the alleged plagiarism. 
The court in Haarlem ruled in November 2016 that Bakker had not committed plagiarism. The judge found that her book and that of Pols are ‘in their nature’ similar, but found that understandable because the two followed their training as weight consultant and nutrition coach at the same time and thus acquired the same knowledge. The court ruled that the overall impression of the books, on the other hand, is completely different.
In 2008, researchers from Wageningen University published the results of a 40-week scientific study into four different ways to lose weight. Some of the research groups ate according to instructions from Bakker’s diet books. A second group followed the program of [Ladyline. The third group received monthly guidance from a dietician and the fourth group only received an information brochure from the Nutrition Center. The control group that used Bakker’s books scored the lowest, together with the group that used the information brochure of the Nutrition Center. They lost an average of 4% body weight in 40 weeks. The group that visited the dietician every month lost an average of 7% and the group that followed the Ladyline intensive program became on average 12% lighter.
Popularity is declining
In May 2009, Bakker’s popularity as a diet guru seemed to stagnate. Insurer Univé has stopped its special Sonja Bakker policies due to a lack of interest. Launched on September 23, 2008, Sonja magazine rapidly declined in popularity. More than 200,000 copies of the first edition were sold. After six months, that number has halved to 100,000 per issue. The last Sonja was released in November 2009.  Sales of her books are down more than 80 percent in 2008. Bakker herself initially denied that the hype surrounding her person was over.  At the end of September 2009, it announced that it would cease most of its activities with effect from 2010.   After 2010 new books were published about weight loss and she started a Bed & Breakfast in Hoorn with her second husband, this B&B was closed again in March 2014.
In 2010 Sonja Bakker published two children’s books at publisher De Zonnestraal.
- 2005 – Reach Your Ideal Weight! ; [Part 1]: An effective weight loss program
- 2006 – Reach Your Ideal Weight for Kids and Teens! An effective program to lose weight responsibly.
- 2006 – Achieve and maintain your ideal weight!
- 2007 – Summer Slim with Sonja
- 2007 – Healthy enjoyment with Sonja
- 2008 – Happy in your own skin with Sonja! in collaboration with fashion chain Miss Etam  
- 2009 – Expand your boundaries: with Sonja and Rik on a culinary safari, with co-author Rik Felderhof
- 2010 – The Adventure Mom
- 2010 – Craft Diary
- 2011 – Pure yourself: insight diary
- 2011 – Reach Your Ideal Weight !; Part 2
- 2012 – Reach Your Ideal Weight For The Whole Family!
- 2013 – Ibiza, Heaven and Hell (novel)
- 2013 – Winterslank
- 2013 – Reach Your Ideal Weight For The Whole Family / Part 2
- 2014 – Reach Your Ideal Weight For The Whole Family / Part 3
- 2015 – Reach Your Ideal Weight For The Whole Family / Part 4
- 2017 – Reach Your Ideal Weight For The Whole Family / Part 5
- 2017 – Bikini proof with Sonja
- 2017 – Sonja’s Bella Italia!
- 2018 – Slimmer slim with Sonja
- 2019 – Summerproof
- 2020 – Streetfood