The Science Behind Popular Diet Trends
Dieting is a very common practice that many people engage in at various points in their lives. The popularity of dieting is fueled by several factors, the first being a national aversion to being overweight. In today’s social media run society, we are constantly inundated with transformation posts and videos of people who have lost a lot of weight from various diet plans and some of us want to be a part of that trend. Many of us also want to experience fast results. However, many of these trendy diets do not have the evidence to back up their effectiveness and safety. That’s not to say that some of these diets are not effective if applied properly and consistently. However, many of them are not lifestyle-based diets and eventually get phased out of our daily activities.
Research suggests that most diet programs have very short term effects on helping people lose weight and improve their cardiovascular health. One study showed that over six months most macronutrient diets resulted in modest weight loss and substantial improvements in cardiovascular risk, particularly with blood pressure. However, at 12 months the effects on weight reduction and improvements in cardiovascular risk factors largely disappear.
In the sections below, we will explore a variety of diets that have been researched for their effectiveness in weight loss and weight regain prevention. Each of these diets have overlapping restrictions that support claims of preventing obesity however, the science challenges these claims indicating that it may cause more harm over the long term.
Keep reading to learn more...
Calorie Deficit Diets
Diets that are structured around a calorie deficit typically aim at reducing calorie intake by 500-750 kcal for a daily intake around 1200–1500 kcal/d for females and 1500–1800 kcal/d for males. These diets generally follow the macronutrient composition of: 30% fat, 50% carbohydrate and 20% protein, with a particular emphasis on reducing intake of saturated (animal-derived) fat and increasing intake of fiber-rich foods such as fruit and vegetables. The latter can both promote satiety and provide a great variety of beneficial micronutrients.
Studies show that calorie deficit diets can lead to a modest weight loss of approximately one pound (0.5 kg) per week or nearly five pounds (2 kg) per month. This weight loss is usually seen only in the first months, since the rate of weight loss is expected to slow down due to hormonal adaptations resisting weight loss. Although calorie deficit diets are modestly effective for short-term weight loss, individual results vary and long-term adherence to these diets is difficult to accomplish.
Low Fat Diets
There has been a lot of controversy about low-fat vs. high-fat diets and their effect on weight loss. Traditionally, low-fat diets have been recommended as safe and effective weight loss strategies because:
Energy from fat is less satiating than energy from carbohydrate, and a high fat/carbohydrate ratio in the diet can promote passive overconsumption and weight gain in susceptible individuals
Fat is more readily absorbed from the intestine than carbohydrate and fecal energy loss is much lower with a high dietary fat/carbohydrate ratio.
Carbohydrate is more thermogenic than fat and energy expenditure is lower during a diet with a high fat/carbohydrate ratio than during a diet with a low fat/carbohydrate ratio.
A high-fat diet may damage the intestinal barrier and cause intestinal dysbiosis with an adverse impact on body weight and metabolic variables. This can result in hormone imbalances and associated diseases.
A single gram of fat contains more than twice the calories of a gram of carbohydrates or protein (9 kcal/gram vs. 4 kcal/gram). Thus, reducing total fat intake may theoretically lead to a considerable effect on total amount of calories consumed.
Nevertheless, studies have yet to consistently prove that low-fat diets are more effective in long-term weight loss. One study indicated that both low-fat and higher-fat diets have similar effects on weight loss, total and visceral fat loss, and lean body mass preservation. In this study, both diets were characterized by low intake of saturated fat and foods of high glycemic index and an increased intake of fiber-rich foods, suggesting that when standards of a high-quality diet are met, variations in macronutrient composition play a secondary role for weight loss.
Low Carbohydrate Diets
Research on the efficacy of low-carbohydrate diets provides conflicting evidence. Many low-carbohydrate diets restrict intake to around <30g/d and increase in fiber consumption. One meta-analysis showed that very low carbohydrate ketogenic diets are more effective short-term than other diets for weight loss and improvement of metabolic variables in patients with diabetes. Another meta-analysis found that low-carbohydrate diets enable equal weight loss short-term as isoenergetic balanced or low-fat diets. A third meta-analysis suggested that low-carbohydrate diets led to greater weight loss than low-fat diets, however, benefits should be measured against potential risks correlated with low-density lipoprotein (LDL) cholesterol increase.
Long-term compliance to low-carbohydrate diets is both difficult and potentially dangerous since a significant reduction of carbohydrate intake in combination with high fat intake may lead to increased LDL cholesterol levels and a high mortality risk. A fourth meta-analysis also suggested that low-carbohydrate diets without calorie restrictions are as effective as calorie-restricted low-fat diets in weight loss, emphasizing potential favorable effects on triglycerides and high-density-lipoprotein (HDL) cholesterol levels. However, evidence on the long-term safety and efficacy of these diets is insufficient to support their long-term use.
High Protein Diets
Research on high-protein diets suggest that they deliver 15-20% weight loss results due to their satiety-promoting, lean body mass preservation, and increased thermogenesis benefits. Weight loss studies in overweight women indicate that high-protein diets have positive effects on body composition, blood lipid profile, and glucose homeostasis.
Research also indicates that in overweight patients with Type 1 and Type 2 diabetes, a high-protein diet consisting of 28-30% protein led to weight loss over 12 weeks, particularly in women. However, evidence showing that high-protein diets result in long term benefits is limited and inconsistent. Evidence on the optimal amount and sources of dietary protein is also controversial. Many sources of protein are high in saturated fat, low in nutritional composition, and can increase risk of cardiovascular disease. Animal-derived proteins have been positively associated with obesity and increased risk of nephrolithiasis (kidney disorders), diabetes mellitus and atherosclerosis (clogged arteries), as well as progressive kidney damage in susceptible individuals. It is recommended to partially replace refined carbohydrates with protein sources that are low in saturated fats.
Formula diets are an evidence-based intervention in weight management and are commonly referred to as very-low-calorie diets (VLCD, <800 kcal/d) or low-calorie diets (LCD, 800–1200 kcal/d). They consist of ready-to-consume meal replacements such as nutrient-enriched bars, soups, and drinks, which are low in carbohydrate and fat, and rich in vitamins, minerals, and proteins of high nutritional value.
Formula diets can result in substantial weight loss of 20-40 pounds (10–20 kg) within 8–12 weeks followed by strategic weight loss maintenance and weight regain prevention protocols. These include high-protein diets, anti-obesity drugs, partial use of meal replacements, and high levels of physical activity. Once the desired weight loss is achieved, food is gradually reintroduced so patients can return to a healthy and balanced dietary plan. The additional benefits of this diet includes increases in circulating blood ketones reducing insulin in the blood leading to longer satiety and higher compliance with weight management tools.
Keep in mind that formula diets are intended for a maximum of 12 weeks and should be always applied in carefully selected patients under ongoing medical supervision accompanied by sufficient education and psychological support. Studies suggest that formula diets may deliver significant weight loss and health benefits for patients with diabetes, osteoarthritis, obstructive sleep apnea, psoriasis, and more commonly, in the pre-operative period of morbidly obese patients who are planned to undergo bariatric surgery, since the reduction of liver size achieved by VLCDs may aid the surgery.
Intermittent fasting (IF) also referred to as intermittent energy restriction (IER) is based on the periodic restriction of food consumption. This includes designated hours of either reduced or restricted food intake and alternating hours unrestricted feeding. Researchers have mostly studied IER regimens of two consecutive days per week where on one day there is 60-70% energy restriction and complete fasting on the second day. This is known as the 5:2 regimen however, other regimens are used as well including alternate days, five consecutive days per month, energy restriction by 60–70% or complete fasting.
So far, there are limited studies pointing to the superior or equal long-term safety and efficacy of IER diets compared to traditional calorie-deficit diets. Randomized studies comparing intermittent with continuous calorie-deficit diets in overweight and obese patients, report equal efficacy in terms of weight loss for a period up to 6 months. There are currently no studies suggesting that IER prevents weight gain in normal-weight individuals. Notably, some studies in animal models and normal-weight humans have shown detrimental effects of intermittent diets on metabolic homeostasis, raising safety concerns and the need for further research. IER is generally preferable compared to complete intermittent fasting, due to its higher compliance, lower stress response and milder metabolic fluctuations of free fatty acid and ketone fluxes.
The increasing popularity of IER and IF diets address the need for further rigorous research with appropriately designed, long-term, randomized studies in several subgroups of patients. Currently, there is not enough evidence to determine the optimal macronutrient composition of such diets and multiple knowledge gaps remain.
Diet Quality Research
The general rule that weight loss requires a negative energy balance with energy intake being lower than energy expenditure is both well-established and widely accepted. This concept was further studied in a randomized clinical trial (DIETFITS trial) of 609 overweight/obese and non-diabetic adults (age 18–50 years, BMI 28–40 kg/m2) conducted in Stanford University.
Participants were randomly put on either a healthy low-fat or a healthy low-carbohydrate diet monitored by an intensive dietician-guided training to eat healthy, minimally processed, whole foods cooked at home, without any caloric limits. This study found that both diets delivered a significant weight loss of 11 pounds (5.3 kg) for low-fat and 13 pounds (6 kg) for low-carbohydrate over one year with similar improvement in waist circumference, body fat, fasting glucose and blood pressure. Moreover, the results were independent of genotype patterns or carbohydrate tolerance assessed by insulin secretion.
Researchers concluded that diets with low intake of added sugars and highly processed foods and high intake of fruit, vegetables and whole-grain products, independent of energy intake, is fundamental for weight loss in overweight and obese adults. Also, the prediction of efficacy based on genetics or insulin response to carbohydrates is not currently possible due to the limited number of candidate genes assessed and requires further research.
Which of these diets have you tried? What was your experience? Leave a comment below.