PEN® eNews 16(1) January 2026 - Fad Diets

Should Low- or Very Low-Carbohydrate Diets be Recommended for Healthy Adults with Higher Weights? 

What are the effects of low carbohydrate diets (LCDs), including very low carbohydrate ketogenic diets (VLCD, <50g/day), on body weight and cardiovascular disease risk factors among healthy adults with higher weights?

There is probably little to no difference in body weight or cardiovascular risk factors in adults with higher weights who follow a weight-reducing low carbohydrate diet (LCD) compared to a weight-reducing balanced carbohydrate (CHO) diet for up to two years. Although small differences in body weight and blood lipid levels were observed, these are unlikely to be clinically important.   

Following a very low carbohydrate ketogenic diet (VLCD) for up to 12 months in adults without chronic disease may result in reductions in body weight, blood pressure, triglyceride levels and glycemic control but may increase total cholesterol and LDL-C levels compared to a non-ketogenic diet.    

Adverse effects of LCDs and VLCDs were poorly reported. Individuals following a LCD or VLCD should be monitored for possible adverse effects (e.g. gastrointestinal, headache, fatigue, anxiety, mood disturbances, depressive symptoms).

Remarks

The definition of lower carbohydrate diets vary. The macronutrient composition of the most common diets included in the studies were:  

• Ketogenic diet: <10% energy from CHO or <50 g/day CHO; unspecified fat, protein and energy intake. 

• Non ketogenic diet: >10% energy from CHO or >50 g/day CHO; unspecified fat, protein and energy intake. 

• VLCD: <10% of energy from CHO, unspecified fat and protein. 

• LCD: <45% of energy from CHO, balanced fat (20-35% of energy) and high protein (>20% of protein). 

• Control: balanced for CHO (45-65% of energy), fat (20-35% of energy) and protein (10-20% of energy).

To see the full practice question, click here.

Can an Alkaline Diet Prevent or Treat Chronic Disease?

Does an alkaline diet have a role in the risk, prevention or treatment of chronic diseases such as obesity, cardiovascular disease, hypertension and diabetes?

A recommendation about the use of an alkaline diet to prevent or treat obesity, cardiovascular disease, hypertension or diabetes cannot be made because evidence is not available.

Limited evidence from observational studies suggests that a high dietary acid load is associated with higher blood pressure, serum insulin, obesity prevalence and diabetes risk and prevalence, but a conclusion about causation cannot be made.

Remarks

An alkaline diet has a low dietary acid load and emphasizes the consumption of alkaline-producing foods, such as vegetables, fruit, nuts and legumes and limits the consumption of acid-producing foods including meat, poultry, dairy products and refined grains.

To see the full practice question, click here.

What is the Paleolithic Diet?

PEN Backgrounds are a great place to start when a client asks you about a diet that you may not know much about. You’ve probably heard of the paleolithic diet - but do you know its history and all of the foods it includes? Here are some highlights from our Diet Composition - Paleolithic Diet Background.

• The Paleolithic diet is a pattern of eating that attempts to mimic what humans ate during the Paleolithic period, which predates the agricultural revolution. It was developed by Loren Cordain in the early 2000s and was inspired by articles published by Dr. Stanley Eaton in the 1980s that suggested that because the human genome has not changed significantly in the last 10,000 years, humans are not adapted to eating many of the foods that make up the modern diet (e.g. grains, legumes and processed foods) and that individuals should therefore strive to eat the same way humans did during the Paleolithic period.

• There is no agreed-upon definition of the Paleolithic diet, although it generally permits the consumption of lean meats, fish and seafood, fruit and non-starchy vegetables and excludes all cereals, legumes, tubers, dairy foods and processed foods.

• It is difficult to truly understand what Paleolithic humans ate, but anthropological research suggests that it was likely a variety of plants (including tubers, seeds, nuts, barley, legumes and flowers), animals (mainly small game animals), seafood (particularly in coastal regions), insects and honey and that their diets were dictated by the local environment, season and food availability. There is likely not one single Paleolithic diet but rather a diversity of Paleolithic diets.