Nutrition • 4 Dec 2020
Science and Evidence Supporting Healthy Eating
By Bavani Nadeswaran, MD, MBBS
Lead SSIHI Integrative Weight Management Program
UC Irvine Health Internal Medicine
Obesity is a serious health problem, and the prevalence of obesity continues to increase among adults in the U.S. The prevalence of obesity was 42.4% in 2017 – 2018[i]. Obesity can lead to type 2 diabetes, heart disease, and multiple cancers. Although cardiovascular mortality rates have improved[ii], the decline in mortality has recently ceased, and there has been an increase in mortality in 35- to 64-year-old males and females in the United States[iii]. Obesity along with poor diet are important, modifiable contributors to the rise of cardiovascular disease with an estimated attributable risk of 13% to cardiovascular mortality[iv].
When it comes to healthy eating, we all want easy solutions. Nutrition science is imperfect and is constantly evolving. For example, in the ‘80s, recommendations to follow a low-fat diet, lead to increased consumption of high-sugar food which subsequently evolved into a public health crisis and exponential increases in the rates of diabetes. When it comes to combatting diabetes, current research shows that losing 5-10% [v]of body weight and maintaining this weight loss is correlated with lower risk for diabetes and reduced cardiovascular mortality.
There are several dietary interventions that have been shown to improve cardiovascular risk; one of these is caloric restriction, which involves limiting calories consumed during a specific period of time. Caloric restriction is linked to improvement in weight, blood pressure, and insulin sensitivity in humans.
Daily fasting schedules have become one of the most popular methods to achieve caloric restriction and has been effectively employed as a weight-loss technique. These fasting schedules, also known as intermittent fasting, have been linked to considerable overall health benefits according to a recent article in the New England Journal of Medicine[vi].
There are two main types of intermittent fasting, alternative day fasting and time-restricted fasting. In alternative day fasting, there is a focus on having lighter caloric intake for certain days of the week. In the 5:2 strategy there are 2 fast days mixed into 5 nonrestrictive days. For time-restricted fast programs, variations include 16-hour fasts with 8-hour feeding times each day. Intermittent fasting has been linked to glucose control in both humans and animal studies. Intermittent fasting is often associated with an overall decreased caloric intake but is not integral to its efficacy. Long-term adherence to caloric restricting diet is low, whereas adherence to intermittent fasting may be more promising.
Intermittent fasting may exert its effects through multiple pathways.
- Reducing oxidative stress, the oxidative stress hypothesis states that decreased energy intake causes mitochondria to produce fewer free radicals[vii].
- Optimization of circadian rhythms. Fasting properly may allow optimization with our organs’ peripheral clocks such as those in the liver, adipose, and skeletal tissues. Dysregulation of this system increases the risk for chronic diseases[viii].
- Ketogenesis, after 6-8 hours of fasting, ketone levels become detectable, which signals a switch from fat storage to fat use with a decrease in low-density lipoproteins (LDLs) and an increase in high-density lipoproteins (HDLs) levels. Ketone bodies stimulate expression of the gene for brain derived neurotrophic factor with benefits for brain health, psychiatric and neuro-degenerative disorders[ix].
A recent study from UCSF[x] compared an intermittent fasting group to a control group that did not curtail eating to a restricted time. The weight loss between the 2 groups were not different. Classically intermittent fasting should follow the biological circadian rhythm with an eating window between 10AM-6PM; this study fasted patients between noon to 8PM. Thus, it is not entirely clear if the results of this study indicate that time restricted diets are not effective or whether it is more important to consider fasting that follows the biological circadian rhythm. This study found in the time restricted eating group there was a slight decrease in appendicular lean mass. This could be a result of missing morning protein intake or technical error with lean mass assessment when the weight change is small.
Hippocrates said, “Let food be thy medicine, and medicine be thy food”, emphasizing the importance of eating a balanced diet. Regardless of how you choose to diet, there is an undeniable impact that healthy eating has on overall health. Eating 6- 8 serving of fresh fruits and vegetables, whole grains, beans, legumes, and, if desired, a healthy portion of fish, chicken, and low-fat dairy products will always be a recipe for healthy weight loss and a healthy life because these foods are dense with vitamins, minerals, protein, healthy fat and fiber. It is also important to be mindful of the practice of eating; when we focus on the experience of eating we actually feel more pleasure and satisfaction from food, and are less likely to overeat.
[i] NCHS Data Brief No. 360, February 2020
[ii] Lloyd-Jones DM, Hong Y, Labarthe D, et al; American Heart Association Strategic Planning Task Force and Statistics Committee. Defining and setting national goals for cardiovascular health promotion and disease reduction: the AHA’s strategic Impact Goal through 2020 and beyond. Circulation. 2010;121(4):586-613.
[iii] Klein RJ, Schoenborn CA. Age Adjustment Using the 2000 Projected US Population. Hyattsville, MD: National Center for Health Statistics; January 2001. Healthy People Statistical Notes, No. 20.
[v] National Heart and Blood Institute. Managing overweight and Obesity in adults: Systematic evidence review from the Obesity Expert Panel. https://wwwnhlbinigovv/sites/default/files/media/docs/obesity-evidence-reviw.pdf.2013.
[vi] Effects of Intermittent Fasting on Health, Aging and disease; https://www.gwern.net/docs/longevity/2019-decabo.pdf
[vii] Merry BJ. Oxidative stress and mitochondrial function with aging–the effects of calorie restriction. Aging Cell. 2004; 3: 7-12
[viii] Gill S, Panda S. A smartphone app reveals erratic diurnal eating pattern in humans that can be modulated for health benefits. Cell Metab. 2015; 22(5):789-798. Doi:10.1016/j.cmet.2015.09.005
[ix] Dashti HM; Al-Zaid NS; Mathew TC; et al. Long term effects of ketogenic diet in obese subjects with high cholesterol level. Mol Cell Biochem. 2006; 286: 1-9
[x] JAMA Internal Med. Published online September 28, 2020. Dylan A. Lowe, PhD; Nancy Wu, MS; Linnea Rhodin-Bibby, BA; et al