Which Diet Works? Part I

A ground breaking research study was done in 2017 which compared all of the major diets including: high carbohydrate/low fat, ketogenic diet, high protein, intermittent fasting, and daily caloric (energy) reduction.

Is there one diet that works better than another for the majority of people?

Is losing weight as simple as calories in being lower than calories out?

Alan Aragon and others put together a large research study examining these questions in 2017. You can access the entire study here, but I’ll break it down for you into the most useful information I found from the research. It’s important to note that this research is only studying the results of body composition and doesn’t include overall health effects.

Part one of this blog series compares the research of popular diets. Part two will focus on the concept of calories in/calories out being the primary mechanism for weight loss. Let’s dig in.

Low Fat/High Carbohydrate Diets

“A recent systematic review by Hooper et al. analyzed 32 randomized controlled trials containing ~54,000 subjects, with a minimum duration of 6 months. Reducing the proportion of dietary fat compared to usual intake modestly but consistently reduced body weight, body fat, and waist circumference.”

Take a look again at how many people were in this study — 54,000 — that’s a huge trial! The proportions of fats to carbs were about 20–30% fat and 45–65% carbs. This sounds great, right? Over six months there was consistent reduction of weight, body fat, and waist size — perfection! Not so fast…

“ over the long-term, diets with lower energy density have not consistently yielded greater weight loss than energy restriction alone.”

What does this mean? After the six month trial, when you continue this type of diet the weight loss tapers off. The overall weight loss ends up in the long term being no different than if you just lowered the number of calories (regardless of if it’s low fat, high carb, low carb, high fat). The researchers hypothesize that this is because of the body learning to compensate for the dietary change.

The next study took the fats even lower so that the consumption is 10–20% of daily calories. The researchers noted that this trial was aimed more at weight loss for vegans and vegetarians and not necessarily measuring entire body composition. This is important because it means they were looking at the number on the scale but not at the amount of muscle loss compared to fat loss. The results of this study were interesting. The researchers basically couldn’t trust the results because the subjects over the 12 month period actually had a fat intake average of 21–29% of daily calories. They could not keep the fat intake low enough.

“…actual intake progressed from 21.1 to 29.8% by the end of the 12-month trial.”

Since the low fat and very low fat diets actually ended up with similar amounts of fat intake this next conclusion shouldn’t be too surprising.

“No significant between-group differences were seen in the loss of total abdominal, subcutaneous, or visceral fat at either six months or two years.”

Low Carbohydrate Diets

Low carb diets are those which have a maximum of 200 grams of carbohydrates daily (not the Ketogenic diet which has even lower carb consumption). This one I’m going to go over quickly because the research was done on very obese subjects which didn’t make it applicable to the majority of adults. The authors of this research also noted the results are not significant for the majority of people.

Breaking this down, basically the low carb diet worked well for very obese people in the short term. For most us though, these diets would likely have limited success.

Ketogenic Diet

Keto diets keep the carb intake very low at 50 grams or less daily or approximately 10% of daily calories. Protein intake is moderate and fat intake is high at about 60–80% of daily calories.

The results of these studies were very interesting. The goal of a ketogenic diet is to increase the body’s utilization of fat as a fuel thus causing fat loss. However, the research has found that the body will actually plateau the amount of ketones in the blood. This happened within just two weeks of the study!

More research found that the results of ketogenic diets were based more on the amount of protein consumed than the fat and carb content.

“…systematically demonstrated that the higher protein content of low-carbohydrate diets, rather than their lower carbohydrate content, was the crucial factor in promoting greater weight loss during controlled hypocaloric conditions. This is not too surprising, considering that protein is known to be the most satiating macronutrient.”

“With scant exception , all controlled interventions to date that matched protein and energy intake between Ketogenic Diet and non-Ketogenic Diet conditions have failed to show a fat loss advantage of the Ketogenic Diet. A recent review by Hall states, ‘There has never been an inpatient controlled feeding study testing the effects of isocaloric diets with equal protein that has reported significantly increased energy expenditure or greater loss of body fat with lower carbohydrate diets.”

In light of this and the previously discussed research, the ‘special effects’ of Low Carbohydrate Diet and Ketogenic Diet are not due to their alleged metabolic advantage, but their higher protein content.

To reiterate a previous point, rigorously controlled isocaloric, protein-matched studies have consistently demonstrated that keto-adaptation does not necessarily amount to a net decrease in fat balance, which is ultimately what matters.

Does Keto work? In the short term it can suppress appetite and cause a loss of water weight. The problem for long term use is that, just as with any other macronutrient manipulated diet, the body will adapt to the use of fat as a fuel and become really good at using fat (thus the plateau). Conversely, when you reintroduce carbohydrates the body will not be used to using it as a fuel and tend to store it as fat until adaptation occurs.

High protein

Raising protein in a calorie deficit was by far the most successful method of improving body composition. High protein is defined as ranging from 1.2-1.6 g/kg of bodyweight.

Three studies were done where subjects had various protein intake including: 0.8 g/kg (U.S. recommended daily allowance), 1.6 g/kg , and 2.4 g/kg of bodyweight. This study was held in a metabolic ward where everything they ate was provided and allowed for very reliable research settings. The research participants were not allowed to exercise during the 8 week period and were in a hypercaloric state.

The results showed that all three groups gained similar amounts of fat. However the group with the lowest protein intake (0.8 g/kg) lost 0.7 kg of lean mass (muscle). The group which consumed 1.6 g/kg gained 2.7 kg of lean mass and the 2.4 g/kg group gained 3.9 kg of lean mass.

These astounding results show the benefit of high protein intake during a calorie deficit in order to maintain muscle mass.

“a succession of recent meta-analyses supports the benefit of higher protein intakes for reducing body weight, fat mass, and waist circumference, and preserving lean mass in an energy deficit.”

Intermittent Fasting

There are several forms of intermittent fasting including: time-restricted feeding, alternate day fasting (fasting for 24 hours then returning to normal eating for 24 hours, etc.), and whole day fasting (fasting one to two days per week and the rest of the week maintaining an appropriate calorie range).

The various forms of intermittent fasting were studied and compared to a continuous energy restriction. The continuous restriction is a daily calorie deficit where the calories consumed are only slightly decreased. The research of this comparison showed that in the long term both intermittent fasting and continuous energy restriction had the same results.

“Seimon et al. recently published the largest systematic review of IF research to date, comparing the effects of intermittent energy restriction (IER) to continuous energy restriction (CER) on body weight, body composition, and other clinical parameters. Their review included 40 studies in total, 12 of which directly compared an IER with a CER condition.

They found that overall, the two diet types resulted in “apparently equivalent outcomes” in terms of body weight reduction and body composition change. Intermittent fasting failed to result in superior improvements in body composition or greater weight loss compared to continuous energy restriction.”

So there you have it. All the major diets compared to simply creating a small calorie deficit each day. Take what you want from the research but I’ll tell you what stood out to me.

When it comes to weight loss and body re-composition efforts the style of diet matters much less than the fact that you are in a calorie deficit. There is no magical diet that will make you forever lean. The most important thing you can do is to increase protein intake. This was an across the board finding with all of the studies. As long as protein was kept at a reasonable range (above the RDA) lean mass can be retained and people are more likely to sustain the calorie deficit.

There is a such thing as too low of a calorie deficit. Going too low can have potentially detrimental effects on your body’s long term metabolism. That is what we will discuss in Part II of the diet comparison study. Stay tuned.