What was your New Year’s resolution? If I had to take a guess, I would say it had something to do with weight. Many people aim to lose weight in the new year, and I get asked all the time about the best diet for weight loss. Unfortunately, there isn’t one perfect diet for everyone to lose weight.
I wanted to take some time to explore what the research is showing regarding the four most common diets people ask me about for weight loss- Paleo, ketogenic, vegan, and intermittent fasting.
What is the paleo diet?
The Paleo diet is a diet based on what our early ancestors would have most likely eaten. The diet is rich in meat, fish, leafy and cruciferous veggies, root veggies, eggs, nuts, seeds, and fruits. The diet excludes dairy, grains, beans and legumes, processed foods, and refined oils and sugars. Many people think paleo is meat only, but if you look at the list above- there are a lot of produce options (that many people “forget” to include in a Paleo diet). The standard American diet can contain up to 70% of daily calories provided by foods that our ancestors were not consuming including grains, refined sugars, and highly processed fats1. The paleo diet is claimed to decrease inflammation while improving diabetes, blood pressure, and blood lipid levels.
What does the research say about paleo and weight loss?
Observational studies of hunter-gathers do support the notion that a paleo style diet might reduce the risk of cardiovascular disease, type 2 diabetes, cancer, and metabolic syndrome2. One study compared blood glucose in a Paleo diet versus a Mediterranean-style diet. The Paleo style group decreased blood glucose by 19% MORE than the Mediterranean group. This group also lost 2.2inches average around the waist over 3 months3. Another study, comparing the standard diabetic diet and the Paleo diet, found a significant decrease in blood sugar, triglycerides, blood pressure, weight, BMI, and waist circumference in the Paleo group4. The Paleo group decreased their weight by almost 7lbs over a 3-month period. This weight-loss pattern was also confirmed by Osterdahl et al and Ryberg et al, who showed a decrease in weight of about 5-10lbs over 3-5 weeks in test subjects following a paleo style diet5,6. One theory as to why this might happen is that consumption of a paleo diet can be associated with a decrease in calories (even when participants could eat as much as desired6. The emphasis on veggies and protein with a limited amount of carbohydrates (mostly from produce sources) often helps people feel full while reducing the number of calories consumed resulting with weight loss. The Paleo diet (when done with the supervision of a dietitian or another health professional) can be rich in protein and fiber which is very satisfying and therefore also helps to decrease calorie intake resulting in weight loss.
What is the ketogenic diet?
The ketogenic diet is an increase in the consumption of dietary fat while decreasing carbohydrates to encourage the body to run on fat as the primary fuel source. Traditionally, carbohydrates are kept at less than 50 grams per day, with primary sources from veggies and fat counting for 70-90% of calories. The premise of running on fat is not new. Anytime you fast- your body begins to use your fat stores for energy. The idea of a ketogenic diet is that by providing low carbohydrates, you encourage the body to run on your own fat stores during periods of fasting (ie overnight, between meals, etc) to promote weight loss.
What does the research say about ketogenic diets and weight loss?
Most of the research on the ketogenic diet is on seizures, but research is also being done on ketogenic diet and weight, cardiovascular disease, diabetes, cancer, Alzheimer’s disease, autism, PCOS, and autism. Several studies have shown the benefit of a ketogenic diet to support weight loss. A study by Tendler et al showed an average weight loss of about 28lbs in patients with nonalcoholic fatty liver7. Another study showed that low-carbohydrate dieters lost more weight (~4% more weight) than those on a low-fat diet over 3 and 6 months. This group also had an increase in HDL and a decrease in triglyceride levels8. Similar findings on blood lipids were also discovered by Samaha et al and Brinkworth et al. This study again, found that a low-carbohydrate diet decreased triglyceride levels and improved insulin sensitivity when compared to a low-fat diet. This study also found that these results were irrespective on the use or nonuse of lipid-lowering medications9,10. These studies all showed that consumption of higher levels of fat not only did not worsen lipid levels, but actually improved them. McClernon et al proposed that weight loss was related to an increase in satiety on a ketogenic diet over a low-fat diet11. Consumption of higher fat was associated with less hunger and therefore less desire to eat excessive calories. Less hungry = less calories consumed = more weight loss. Sounds like a good equation to me!
One very interesting study found that consuming a ketogenic diet can help you get rid of that tummy quicker. A study completed by Volek et al, showed that consumption of a ketogenic diet increased the fat lost in the trunk [FIGURE 1] (sorry women, men seem to get more benefit but still regardless of gender- the ketogenic diet was more efficient at getting rid of that stubborn tummy) 12.
What is a Vegan diet?
A vegan diet is the consumption of no animal proteins or products. Vegan diets are rich in veggies, fruit, beans, legumes, and grains. Vegan diets have been researched to have health benefits for
A vegan diet is the consumption of no animal proteins or products. Vegan diets are rich in veggies, fruit, beans, legumes, and grains. Vegan diets have been researched to have health benefits for cardiovascular disease, hypertension, cancer, and diabetes. Because of the heavy reliance on produce for a bulk of the diet, vegan diets can be very rich in fiber, vitamins, minerals, and antioxidants. They are also often very low in trans fats and refined carbohydrates. Vegan diets can be very safe and even beneficial when thoughtfully initiated to prevent deficiencies in B12, protein, iron, zinc, calcium, vitamin D, and iodine.
What does the research say on the vegan diet and weight loss?
There are several studies supporting a vegan diet for weight loss. A study by Mishra et al, showed a 6lb weight loss over 18 weeks on a vegan diet with a decrease in LDL, total cholesterol, and average blood sugars (HbA1C)13. A very large study (37,875 participants) by Spencer et al, found that vegans had the lowest BMI followed by fish eaters and vegetarians. Meat eaters had the highest BMI. High protein and low fiber were the dietary factors that were most associated with BMI14. In another study on patients with polycystic ovarian syndrome (PCOS), a vegan diet (with nutritional counseling) lost significantly more weight, and those that were more engaged with an accountability group lost the most15. The vegan diet might be beneficial for weight loss due to the increase in fiber content. Fiber can help to decrease appetite and consumption of high fiber is associated with more weight loss16.
What is intermittent fasting?
Intermittent fasting (IF) might be an alternative to calorie restriction. IF usually involves restricting energy (~75% restriction) on 1-3 days a week and eating freely on the other days 17. Fasting days are usually around 500-600 calories and are often not back to back. For example, you consume less on Monday and Thursday, but eat normally the rest of the week.
What does the research say on intermittent fasting and weight loss?
Recent studies have been showing that IF can be as effective as calorie restriction for weight loss and has a higher level of compliance (meaning you’re more likely to stick to it). A review study found that calorie restriction was more effective for weight loss, but IF had comparable reductions in fat mass, fasting insulin, and insulin resistance17. However, another study found that IF was just as effective as calorie restriction for weight loss and management of type 2 diabeties18. The main benefit is that IF allows you to continue to eat normally most days of the week, while only restricting a few times during that week.
Whew, are you still with me? Are you confused? Yes, the research seems to support ANY of these diets for weight loss.
So, here’s my take away- to support weight loss eat real food, lots of veggies, and not too much. Also, find someone who will support you- whether it is your spouse, a friend, or your dietitian. Weight loss is hard work, and everyone is going to be different on what specific diet works best for them. So, keep in mind, if you didn’t have success- that might not have been the best diet for your body and your specific needs at that phase of your life. If you ever need help deciding the best way to eat for weight loss (or just overall health), reach out to your favorite dietitian (hopefully that’s me) for a recommendation. Most dietitians have lots of training and spend a lot of time with our patients discussing what is going to be the best diet given the WHOLE picture.
Join in the discussion and leave your comments below!