Navigating fad diets for weight loss



LB, a 27-year-old female, would like to lose 10 pounds before her friend’s wedding next month. She has struggled with weight management throughout her life, with a current body mass index (BMI) of 30. With a demanding work schedule, LB often resorts to fast food meals, has little time for physical activity, and increases her food consumption when stressed. She has read positive reviews for the Atkins and Ornish diets, and asks which one you would recommend. LB has no additional health concerns, no known allergies and currently uses the ethinyl estradiol/norelgestromin patch for birth control.


Obesity is a chronic condition resulting from excessive caloric intake and inadequate caloric loss, leading to accumulation of fat in adipose tissue.(1) BMI is a common measure of body fat based on height and weight; a BMI ≥ 30 indicates obesity (Table 1).(2) Obesity rates for Canadian adults have tripled since the 1980s, with rates expected to reach 21% by 2019.(1) Obesity is associated with significant health consequences, including diabetes, cardiovascular disease and some forms of cancer.(3)

A 5%–10% reduction in body weight can produce notable health benefits for obese patients.(4) Fad diets, which involve restricting or eliminating certain food groups, continue to be a popular approach to weight loss. These diets can be categorized into five groups(1,5):

• Low-carbohydrate (e.g., Atkins, Dukan, Montignac)
• Low-glycemic-index (e.g., South Beach, Glycemic Index)
• Low-fat (e.g., Ornish, Pritikin)
• Low-calorie (e.g., Dr. Bernstein, Cambridge)
• Mixed, balanced (e.g., The Zone, Weight Watchers, DASH)

Table 1
Defining weight based on BMI in adults(1)
Body mass index (BMI) (kg/m2) Underweight Normal Overweight Obesity
(Class I)
(Class II)
(Class III)
< 18.5 18.5–24.9 25–29.9 30–34.9 35–39.9 ≥ 40


Case analysis

With the Atkins diet, carbohydrates are initially restricted to < 20 g/day, while foods high in protein (e.g., fish, poultry, eggs) and healthy fats (e.g., olive oil, nuts, avocados) are encouraged.(6) The carbohydrate restriction induces a state of ketosis, where the body begins metabolizing fat for energy.(7) The rapid weight loss commonly seen, however, is likely due to glycogen breakdown and fluid loss, rather than fat metabolism.(7) When dieters are 15 pounds from their weight goal, certain carbohydrates (e.g., legumes, whole grains) are slowly reintroduced.(8) Once the weight goal is reached, dieters are encouraged to target 80–100 g of carbohydrates daily for ongoing maintenance.(9) Concerns with low-carbohydrate diets are related to the induction of ketosis, which can produce renal damage through dehydration and electrolyte imbalance.(1) Other adverse effects include headache, halitosis and constipation.(1)

With the Ornish diet, fat intake is restricted to < 10% of total daily caloric intake,(1) primarily by consuming a plant-based diet (e.g., fruits, legumes, soy products) and eliminating fatty foods (e.g., fish, poultry, oils).(10)

Refined carbohydrates and alcohol are allowed, but not encouraged.(10) With a strong emphasis on portion control and avoidance of hunger through small frequent meals, weight loss may be related to reduced caloric intake, rather than fat restriction itself.(10) Long-term consequences of fat-restricted diets are largely unknown. Concerns include elevated triglycerides, reduced HDL (“good”) cholesterol and impaired absorption of fat-soluble vitamins.(11)

Table 2
Dietary reference intakes for macronutrients and fibre to maintain nutritional balance in adults(1)
Total carbohydrate
(% energy)
Total protein (% energy) Total fat
(% energy)
Omega-6 polyunsaturated fatty acids (% energy) Omega-3 polyunsaturated fatty acids (% energy) Fibre
(g/day, whole grains)
45–65 10–35 20–35 5–10 0.6–1.2 30


Low-carbohydrate diets tend to produce greater weight loss than low-fat diets during the first six months of dieting.(1) However, differences in total weight loss are nonsignificant after one year.(1) Both diets may reduce the risk of metabolic and cardiovascular disease.(7) Unfortunately, the restrictive nature of these diets, and other fad diets, hinder their long-term sustainability.(7)

The best evidence for sustainable weight loss involves reducing caloric intake while maintaining nutritional balance (Table 2).(1) A healthy target for weight loss is 0.5–1 kg weekly, which can typically be achieved by decreasing caloric intake by 500 kcal daily.(4) Other lifestyle modifications, such as reducing stress and increasing physical activity, also aid in weight loss.(1,4)



LB is a candidate for weight loss, as her current BMI places her at an increased risk of health complications. You explain the various options for losing weight, emphasizing the gradual method as the safest and most sustainable approach. LB decides she still wants to lose some weight quickly. As she has no factors, such as pregnancy, that would preclude restrictive dieting, you suggest she try the Atkins diet for rapid weight loss before the wedding, while highlighting potential adverse effects. You recommend that LB then transition to a more sustainable diet—one that is nutritionally balanced, but reduces caloric intake by 500 kcal/day—for long-term weight loss. Decreasing fast food consumption is one way LB could reduce caloric intake. Suggest trying weekly meal preparation to overcome a busy schedule that makes daily food preparation difficult. Encourage 30 minutes of exercise daily and stress-reducing activities (e.g., yoga) to further help LB achieve her weight loss goals.

Nardine Nakhla is a practising community pharmacist and clinical lecturer at the University of Waterloo School of Pharmacy.

The author thanks Kristi Butt, PharmD Candidate 2017 (University of Waterloo), for her contribution to this article.



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11. Lichtenstein AH, Van Horn L. Very low fat diets. Circulation 1998;98:935-9. (accessed March 19, 2017).


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