Study Deep Dive: High Protein Diets and Ultra Processed Foods | Episode 3

In this episode, Dr. Norton breaks down a new study published in Nature titled Short-Term Effects of High-Protein, Lower-Carbohydrate Ultra-Processed Foods on Human Energy Balance. Layne discusses the general structure of a scientific paper and then dives into each section to review the data and determine whether or not he agrees with the authors’ conclusions. Layne also discusses what this means practically and how you can apply the results of this study.

Study: Short-term effects of high-protein, lower-carbohydrate ultra-processed foods on human energy balance

Introduction

Ultra processed foods (UPF) are a contributor to the obesity crisis as they increase food palatability and lead to overconsumption of calories, with each 10% increase in calories from UPFs increasing the risk of obesity by 7%.  1

Additionally, the effect is so dramatic that switching people from a minimally processed diet to an ultraprocessed diet spontaneously increased caloric intake by ~500 kcals per day. 2

Processing food increases the energy density substantially. Research studies demonstrate that UPFs have DOUBLE the calories per gram compared to minimally processed foods (MPFs) (2.2kcal/g vs. 1.1kcal/g). 3 Additionally, UPFs also cost about ⅓ of the price of MPFs ($0.55/100 kcal vs. $1.45/100 kcal)

Due to the low cost, hyper-palatability, & high calorie density, UPFs are major contributors to overconsumption of calories in the USA which based on FAO data is over 3500 kcal/day for the average adult American. 4

Protein is a unique macronutrient in that it provides a source of nitrogen that is required by the body. 

High protein diets appear to have a myriad of benefits, including:

• Improved lean mass accrual and retention 5 6 7 8 9
• Better fat loss ^{6 8}
• Improved satiety, possibly through decreased ghrelin, increased cholecystokini (CCK) and GLP-1 7 10
• Increased energy expenditure, likely due to increased protein turnover & activation of a futile cycle of increased protein synthesis and degradation 11 12 13 14
• Increased rates of muscle protein synthesis (MPS) 6 15

The protein leverage hypothesis also suggests that obesity may be due dilution of protein in the diet. While absolute protein intakes have not dropped, the protein as a percentage of calories in the diet has dropped. The protein leverage hypothesis states that we increase food intake to reach a certain protein level. If protein in the diet is low we will continue to consume calories until this level is reached 16 17

The purpose of this study was to examine the effect of normal protein intake (13% of calories) vs. high protein intake (30% of calories) in the context of a diet high in UPFs

Methods

24 subjects (11 men, 13 women) were randomized to receive either a normal protein, normal carb (NPNC: 13% protein, 46% carbohydrate, 41% fat) UPF diet (84% UPF) or a high protein, low carb (HPLC: 30% protein, 29% carbohydrate, 41% fat) UPF diet (84% UPF) in a metabolic ward where they would be subjected to direct calorimetry. 

They were allowed to consume the diets ad libitum (as much as they wanted) over a 54 hour period and the protein intakes were 1.5g/kg body weight and 3.3g/kg body weight respectively. Both diets were designed to be equal in palatability, fiber, fat, and food type. 

They then went through a washout period of at least 4 days and then consumed the other diet for 54 hours. So each person acted as their own control due to the crossover design. 

Results

The HPLC UPF diet resulted in 196 kcal lower intake per day compared to the NPNC UPF diet. 

Meal duration was also slightly longer with the HPLC diet vs. the NPNC diet

Eating rate and energy intake rate were also slower in the HPLC diet. There were fewer bites per meal and more chews per bite.

The 3 hour post meal AUC for Ghrelin was lower on the HPLC diet vs. the NPNC diet. Ghrelin is a hormone that stimulates appetite. 18 High protein diets have previously been demonstrated to reduce ghrelin. 19

Accordingly, the 3 hour post meal AUC for Peptide YY (PYY) was also increased by the HPLC diet vs the NPNC diet. PYY is a satiety hormone that decreases caloric intake.20 High protein diets have also been demonstrated to increase PYY. 19

24 hour insulin secretion was also greater in the HPLC diet

24 hour energy expenditure was also greater by 128 kcal/day on the HPLC diet

Protein balance was also greater on the HPLC diet vs. the NPNC diet and fat balance was also lower on the HPLC diet vs. the NPNC. 

Both UPF diets resulted in overeating above maintenance with the HPLC overeating by 18% and the NPNC diet overeating by 32%.

Subjective feelings of fullness were also greater on the HPLC diet

Discussion

UPFs caused overeating in this study although the HPLC diet resulted in less overeating than the NPNC diet. Interestingly, the difference in caloric intake on the run in diet (45% UPF) was much more pronounced between the HPLC run in diet vs. the NPNC run in diet. This suggests that the protein leverage may be more pronounced at moderate UPF intake vs. high UPF intake. While the increased protein in the intervention diet was not sufficient to stop the subjects from eating into a positive energy balance, it still tempered the effect. Additionally, the HPLC diet did result it basically a neutral fat balance but positive protein balance which suggests that there was a partitioning effect that was partitioning the excess calories towards lean tissue vs. fat tissue. Unfortunately, due to the short term nature of the study, it’s difficult to make the determination about what would happen over the longer term, but it is in line with other research studies demonstrating that overfeeding with a high protein diet may partition nutrients towards lean tissue. 21

Conclusions

UPF induce overfeeding under both normal and high protein diets. However, the high protein diet did result in a less positive energy balance (18% over maintenance) vs. the normal protein diet (32% over maintenance). This effect was due in part to an increase in energy expenditure (128kcal/d) and a lower energy intake (196kcal/d). The reduction in caloric intake was likely at least in part due to a decrease in ghrelin and an increase in PYY relative to the NPNC diet. The HPLC diet also may have had a partitioning effect towards lean tissue vs. fat. This suggests that high protein diets may be useful under conditions of energy surplus at low, moderate, and high intakes of UPFs.